LANDMARK NEW YORK DEWLLINGS STILL SPEAK OF BUCOLIC TIMES

SUMMER HOME - Harlem Heights: 19 rms Georgian-style mansion, octagonal dining room. On 130 acres, Manhattan's highest pt., superb view all directions. Restored since Revolution. 45 mins. from city. Available for viewing.

THE Morris-Jumel Mansion is no longer on 130 acres, having been enveloped by the city it once was distant from. It is not up for sale, nor are the score of other old - ancient, in terms of modern real-estate development - New York City homes that have been preserved for inspection by present-day house hunters who indulge more in window-shopping than in buying. These homes, scattered about the five boroughs, belonged to people who would be classified today as rich or ''comfortable.'' A condominium, in their day, meant a territory governed by two nations.

There are, among these dwellings, a prosperous merchant's house, now all but lost in the grubby tangle of East Fourth Street; an elegant Bronx mansion just off the main route to Orchard Beach; a house, once the center of a large Dutch farm, still clinging to an acre of greenery that surrounds it in a remote and undistinguished corner of Brooklyn; an old house associated with the country's early struggle for religious freedom, in what is now the Asian heart of Queens, and a lovely house, survivor of Colonial times, that, most improbably, sits on Staten Island at the edge of the Narrows with a breathtaking view of the harbor and the Manhattan skyline.

Many of these landmark houses are in city parks, sometimes having been the reason for starting the park, sometimes having been moved from endangered sites to the protection of the park.

''We're the trustee of these places,'' said Henry J. Stern, the city's Parks and Recreation Commissioner, which is landlord of the 15 houses in the park domain. ''These are houses that were there before the neighborhood changed; in fact, they were the neighborhood. Originally, you might say, New York City was all park. In each case, a historical organization or even the descendants of those who lived there act as caretakers. People can get insights into the city's history in them.''

The list of preserved homes is long, although not nearly so long as preservationists and historians might wish. And the following descriptions of those now open to the public may inspire New Yorkers to seek out other holdovers that speak of more bucolic times in what has become the big city. MANHATTAN The Old Merchant's House 29 East Fourth Street (777-1089)

This house is not in a park, and it was not built in solitary splendor. It was built in 1832 in what was then a fashionable part of town, between Lafayette Street and the Bowery, as one of a group of Greek Revival row houses, and the merchant who bought it was Samuel Treadwell, who dealt in hardware. His youngest daughter lived in it until her death in 1933, when a cousin bought it and preserved it as a museum. The house is distinctive, with a six-step stoop bordered by decorative metal railings leading up to the imposing entrance, and the interior is furnished with the family's furniture, representing the home's century as a residence. The house is very much alive these days with its occasional use for special events and celebrations.

Open 1 to 4 P.M. Sunday. Admission, $2. Appointment required for groups of 20 or more. The Abigail Adams Smith Museum 421 East 61st Street (838-6878)

This is something of a time capsule transported, without ever moving, from the open fields of a 23-acre farm above the East River to the trendy precincts of the Upper East Side, It was built in 1799 as an elegant coach house on the estate of Col. William and Abigail Smith, daughter of President John Adams. The stone building survived the estate's main buildings and was a barn for farm animals, then an inn (with six fireplaces and two porticos) and a private home before being sold to a utility, which surrounded it with three gloomy gas storage tanks. The tanks have gone and, thanks to the Colonial Dames of America, which bought the property, the house has been restored, with Federal-style furniture and a charming little garden.

Open 10 A.M. to 4 P.M. Monday to Friday and in June and July, 5:30 to 8 P.M. Tuesday also. Daytime admission, $2; over-65's, $1; under 12, free. On Tuesday nights, when there are music performances and crafts demonstrations, admission is $3; $2 for the elderly. Gracie Mansion Carl Schurz Park, at East 88th Street and East End Avenue (570-4751)

For all its rush to change, New York, contrarily, installs its seat of power in two of the oldest, most elegant buildings with the most classical lines in New York. One of course, is City Hall, built at the start of the 1800's. The other is Gracie Mansion, built in 1799 and since 1942, official residence of the mayor. Archibald Gracie, a merchant, built it as a country villa overlooking the East River and a view of the Hell Gate shoals. After viscissitudes that saw the structure languish and then serve as the first home for the Museum of the City of New York, it was restored as a home, and reception area for many civic events.

Visitors may walk around outside the house on weekends and appreciate the riverside solitude in which it was established.

Public tours of the interior are available by appointment through November at 10 and 11 A.M., noon and 2, 3 and 4 P.M. Wednesday; special group tours, by reservation, Monday and Tuesday. The fee is $3; the elderly, $1. Hamilton Grange 287 Convent Avenue, at 141st Street (283-5154)

After Alexander Hamilton retired from public life, he and his family, getting away from it all, built this Federal country house and moved into it in 1802, two years before he was killed in a duel with Aaron Burr. The architect was John McComb, whose other projects include City Hall. In 1889, Hamilton's home was moved two blocks south to its present site, just north of City College and sandwiched into a block of brownstones and similar buildings. Since 1962, it has been managed by the National Park Service, which is awaiting Government money to restore the furnishings (sparse at the moment) to reflect its former bourgeois condition.

Open free 9 A.M. to 5 P.M. Wednesday to Sunday. Morris-Jumel Mansion Roger Morris Park, West 160th Street and Edgecombe Avenue (923-8008)

In the midst of a citified neighborhood scenically situated on a high bluff, a delightful enclave suddenly opens up to the wanderer. In its center is a columned white two-story house, all peaks and gables, in a verdant acre-and-a-half setting of trees and garden. The Georgian-Federal mansion was built as a summer home about 1765 by Roger Morris, who, being a Tory, left during the Colonial rebellion. George Washington slept there in 1776 as he commanded his troops in their retreat from the city. (However, during that retreat he had made the troops bite back in the Battle of Harlem Heights, in July 1776, when the British actually gave ground to the Americans.) The mansion's name also recognizes a later occupant, Stephen Jumel, a wine merchant whose widow, Eliza, married Aaron Burr in the front parlor in 1833.

The mansion, which is under the affectionate ministrations of the Washington Headquarters Association, has eight rooms furnished in old-style elegance and open for public visits.

Open 10 A.M. to 4 P.M. Tuesday to Sunday. Admission, $2; students and over-65's, $1; under 12, free. Dyckman House 4881 Broadway, at 204th Street (304-9422)

Manhattan, one must be reminded, was once farm country. The only memento of this bucolic era is on Broadway, far north of the neon firmament for which the street is renowned. The Dyckmans built their farmhouse here in 1783 in a setting near Harlem Creek that is no more. When Broadway was cut through, the house, with its Dutch-influenced gambrel roof and fieldstone lower walls, remained on a slight eminence. Now, without having moved, it sits on its ledge of Inwood marble, now city parkland, with a comfortable open porch that looks at the apartments across the street. It is an intimate dwelling, with a cozy winter kitchen (brick fireplace and Dutch oven), furnished with utensils of early New York times. Other rooms, bed and living, also recall an agricultural life in New York. One room has relics of the American Revolution, which moved past the neighborhood on its way north.

The farmhouse is managed by the Metropolitan Historic Structures Association and is open 11 A.M. to 4 P.M. Tuesday to Sunday. Admission, $1. THE BRONX Wave Hill West 249th Street and Independence Avenue, Riverdale (549-3200)

From the 1830 Federal-style mansion on this 28-acre preserve, home of the Wave Hill Foundation, one gets a breathtaking panorama of the beautiful Hudson River and the Palisades on its far side. Additions have been made to the building, but the sense of lordly remoteness is enhanced by the spaciousness of the grounds. Arturo Toscanini (whose concerts, on recordings, are often presented here), Mark Twain and Theodore Roosevelt are among the notables who have slept here.

Open daily 10 A.M. to 5:30 P.M. through Labor Day. Free except Saturday and Sunday, when admission is $2; over-65's and students, $1; under 14, free. Edgar Allan Poe Cottage Grand Concourse and Kingsbridge Road, Kingsbridge (881-8900)

The Bronx has always prided itself on its salubrious air, superior to that of the lower-lying island boroughs. That's why Edgar Allan Poe in 1846 headed north from choked Manhattan to take up lodging in Fordham. His wife suffered from tuberculosis and died a year later in this rural wooden cottage, which was built in 1812 and for which the poet paid rent of $100 a year. He enjoyed the conviviality in the village taverns and the intellectual stir from St. John's College, which is today Fordham University. He died in 1849, but the cottage has remained, although in 1913 it was moved across the street into the park created for it. The Bronx Historical Society restored it and furnished its small rooms in a way that recalls what a trip to high country meant to New Yorkers in the days before the road extended to the Catskills.

Open 9 A.M. to 5 P.M. Wednesday to Friday, 10 A.M. to 4 P.M. Saturday and 1 to 5 P.M. Sunday; Tuesday by appointment. Admission, $1. Valentine-Varian House 3266 Bainbridge Avenue, between Van Cortlandt Avenue East and East 208th Street, Norwood (881-8900)

No sooner was this house up, about 1775, than its builders, the Valentines, fled with the British from the revolutionists, and a family of farmers, the Varians (Isaac Varian later became the city's 63d mayor), moved in during the 1790's. It is a fieldstone farmhouse, gray and sedate with a sloping roof and shuttered windows, that in 1965 was moved from across the street, where apartment houses were built, to its present site in a tidy park.

The Bronx Historical Society has its headquarters here, and only the lower of the two floors is open to the public to view exhibitions; the current one is on Bronx industry.

Open 10 A.M. to 4 P.M. Saturday, 1 to 5 P.M. Sunday. Admission, $1. Bartow-Pell Mansion, Museum and Garden Shore Road, Pelham Bay Park North (885-1461)

Here is almost buried treasure, a 150-year-old beautiful gray mansion, in Federal style, with formal gardens (a full-time horticulturist is in residence), all but hidden in foliage several yards off the main and heavily traveled road to Orchard Beach. Part of the joy of visiting this house on property purchased from the Indians by Thomas Pell in 1654 is seeing a neo-classic stone mansion with Greek Revival interior in a nine-acre setting consonant with its original surroundings, except for the view of Long Island Sound, which has been obscured by construction.

Under the ministrations of the International Garden Club, the tall-windowed, balconied three-story house has had many of its dozen Greek Revival rooms furnished in appropriate style (half of the items supplied by the administrators, the other half drawn from New York's museums). There is an Empire-style bedroom, all in elegant red trimmings, a bright orangery and a magnificent prospect of spiraling staircases as seen from the ground floor. On the grounds, in addition to flowers, a pool and an herb garden are chestnut, mulberry and fir trees.

Open noon to 4 P.M. Wednesday, Saturday and Sunday. Group tours by reservation. Admission, $1. QUEENS Bowne House 37-01 Bowne Street, at 37th Avenue, Flushing (718-359-0528)

One of New York's oldest homes, this farmhouse was built by John Bowne in 1661. He lived there and also used it as the city's first indoor Quaker meeting place, a situation that placed him in conflict with the Dutch colony's ruler, Peter Stuyvesant, and brought him a victory that gave the house the subtitle of ''shrine to religious freedom.'' Nine generations of Bownes lived in this English-style farmhouse, and it is part of a quiet park enclave in a Flushing neighborhood now throbbing with new energy thanks to a surge in its Asian population. The Bowne Historical Society takes care of the house.

Open 2:30 to 4:30 P.M. Tuesday, Saturday and Sunday. Admission, $1; under 12, 25 cents. Kingsland House 143-35 37th Avenue, at 144th Street, Flushing (718-939-0647)

This 1785 farmhouse was moved in 1965 from a nearby site into Weeping Beech Park, whose huge landmark tree sags mournfully at the building's side. It is only steps away from the Bowne House but has a more distinguished, Colonial profile with Dutch and English features. It is run by the Queens Historical Society, and has antiques and artifacts recalling years of residence by Joseph King, a sea captain, and his successors.

Open 2:30 to 4:30 P.M. Tuesday, Saturday and Sunday. Admission, $1; under 12, 25 cents. The Adriance Farmhouse, Queens County Farm Museum 73-50 Little Neck Parkway, at 73d Avenue, Floral Park (718-347-3276)

Here is a working farm in New York City, in northwestern Queens parkland, with animals and crops and a 1772 farmhouse, Dutch with Victorian additions, sparsely furnished but presenting a unique picture of a rural scene as it might have been before the subways spilled us all out into the environs. It is operated by the Colonial Farmhouse Restoration Society of Bellerose as a museum of agricultural history.

Open 11 A.M. to 4 P.M. Saturday and Sunday. Free except when special events are scheduled. BROOKLYN Pieter Claessen Wyckoff House 5816 Clarendon Road, at Ralph and Ditmas Avenues, Milton M. Fidler- Wyckoff House Park, Flatlands (718-629-5400)

Here, in a three-quarter-acre park in the midst of a drab urban sprawl, is the oldest building within the city limits, one of the oldest frame houses in the United States. It was built perhaps as early as the 1640's but certainly by 1652, when Pieter Claessen Wyckoff, a farmer and the progenitor of the family that lived there until 1902, settled in. It is the most intimate of old buildings, small and storybook-looking with its ski-slope Dutch roof. Thanks to the Wyckoff House Association, it is open as a museum, and visitors may reflect on old New Amsterdam ways as they browse through the eight rooms that were home to those who grew potatoes on its surrounding 200 acres.

Open 10 A.M. to 3 P.M. Friday to Sunday. Admission, $1; over-65's and under 12, 50 cents. Lefferts Homestead Flatbush Avenue and Empire Boule vard, Prospect Park (718-965-6505)

From the ruins of a house destroyed by the British in 1776, the Lefferts family rebuilt, between 1777 and 1783, this appealing and modest home that was moved in 1918 from a nearby street to this site in the park. It is in an intriguing melange of Dutch, English and Federal styles, from the six thin columns on the front porch to the rolling gambrel roof, a construction that the curator calls ''vernacular architecture of the local Dutch tradition not often found in Holland.''

Open free 10 A.M. to 4 P.M. Wednesday to Sunday. STATEN ISLAND Alice Austen House 2 Hylan Boulevard, east of Bay Street, Rosebank (718-816-4506)

The cottage is lovely in itself, but its site is fantastic, at water's edge just north of the Verrazano-Narrows Bridge and with a view of ships sailing past and of the shimmering Manhattan peaks up the bay. From a one-room farmhouse in the 1690's, it was built up into a small gentrified cottage by 1844, when the Austen family moved in. Alice Austen lived here from the age of 2, in 1868, until the mid-1940's, when, impoverished, she had to relinquish it. She was famous for her early work in photography, and 7,000 glass-plate negatives of hers were rescued by the Staten Island Historical Society. The house is historic and endowed with legends, all this with a beautiful panorama at its doorstep and set in a little park with a garden. It is kept up as a museum by Friends of Alice Austen House.

Open 10 A.M. to 5 P.M. Thursday to Sunday. Admission, $2; under 12, free. Conference House 7455 Hylan Boulevard, Tottenville (718-984-2086)

History hangs heavy in this fieldstone manor house built near the island's southern end about 1680 by Capt. Christopher Billop. In September 1776, after the Colonists had declared their independence, they met here with the British, who invited them to discuss a possible peace settlement. The Americans conferred and declined conciliation on any but their own terms and returned to Amboy, N.J., en route to Philadelphia. The house was in private hands for many years and was eventually taken over by the Conference House Association; it survives, well kept, as the only Colonial manor house in the city.

Tours every half-hour from 1 to 4 P.M. Wednesday to Sunday. Admission, $1; children, 50 cents. Richmondtown Restoration 441 Clarke Avenue, off Richmond Road, Richmondtown (718-351-1611)

What better way to conclude browsing historic homes than with a surfeit of them among the two -dozen aged New York City buildings (14 are open to the public) that have found sanctuary in this pleasantly arranged island-center restoration project. In addition to a courthouse, one of the oldest schoolrooms in America and a general store, there are private homes of the 1700's and early 1800's, ranging in style from Dutch Colonial (the 1740 Lake-Tysen House) to modified Greek Revival (the Stevens House and General Store). Other treasures include the 1837 Bennett House and the early 1800's Basketmaker's Shop, which also was residence.

Open 10 A.M. to 5 P.M. Wednesday to Friday, 1 to 5 P.M. Saturday and Sunday. Admission, $2; over-65's and students, $1.50; under 12, $1.

Three other well-known historic homes in the city are temporarily not open to the public because of repairs or restoration. They are the Van Cortlandt Mansion in the Bronx, the King Mansion in Jamaica, Queens, and the Onderdonck House in Richmond, Queens.