If Joseph Baum's fantasy is fulfilled, lovely ladies in long gowns will step onto the maitre d'hotel's terrace, pause for a modest moment, place a hand on the burnished brass handrail with its lead-crystal balusters, and then, on the arm of an escort, flow down the stairs.
Before them, as the dance floor slowly turns beneath a crystal teardrop chandelier, other beauties and their beaus will swirl to ''Isn't It Romantic?''
All about the room, like music-box figurines on the tiers of a wedding cake, waiters in pastel-shaded tails will flambe with great flourish for diners seated at tables laced with silver lame. 'Unabashedly Theatrical'
If all that does not suffice, Mr. Baum might give the signal so that blue and green and red and amber lights within the dome above the dance floor will begin to play.
And then, the Rainbow Room - for decades an elegant icon of New York City in the 1930's - will really be reopened.
''We want it unabashedly theatrical,'' said Mr. Baum, the new manager of the newly resplendent supper club on the 65th floor of the RCA Building at Rockefeller Center.
It may turn out quite like that on Dec. 29, when the Rainbow Room, with its wraparound view of New York's shimmering night skyline, opens to the public after two years of refurbishing.
There will be dress rehearsals this week when, on Wednesday and Thursday nights, David Rockefeller is the host of parties for 800 guests. But the real reopening will be on the 29th.
''It comes after Christmas, sort of a Christmas present from Rockefeller Center,'' Mr. Baum said. ''It will be wine, dine, dance and romance.'' Classy Setting
For many New Yorkers, it will be a chance to remember. ''It has marked the rites of passage for so many generations,'' Mr. Baum said. Not to mention that the Rainbow Room has always been, as he put it, ''one of the great settings for people watching.''
For there in the crowd, if only on that opening night in October 1934, mingled the likes of Noel Coward, Elsa Maxwell and Cole Porter. The Rainbow Room has almost always been that kind of place.
Paul Draper of Woodstock, N.Y., remembers.
Mr. Draper, now 78 years old and only slightly less deft of toe, was a featured performer at the Rainbow Room in the 30's, ''tap-dancing to classical music -Scarlatti, Handel, Bach.''
''Name any socialites you like,'' he recalled, ''they were all there.''
''Everybody had on at least a black tie, if not white,'' he added. ''You couldn't get into the place if you were not formally attired.''
Over the years, the place itself, though always an example of tasteful American Modernism - a step above mere art deco - had become a trifle tattered. And so, two years ago, the Rockefeller Group, which owns Rockefeller Center, set aside $20 million to return the room to its former glory and, at the same time, completely remodel the complex of dining rooms and lounges on the 64th and 65th floors at 30 Rockefeller Plaza.
The design work was done by the architect Hugh Hardy.
Through his renderings, Mr. Hardy said, he has sought to maintain the spirit of Rockefeller Center. American Modernism, he said, is a style ''typified by highly stylized geometric abstraction; the notion of getting down to the underlying order of things.''
And so, throughout the remodeled lounges and suites - other than the Rainbow Room - Mr. Hardy has incorporated bold patterns in deep-set carpeting, hand-crafted cabinetry and paneling of inlaid woods, layered mirror-and-glass ceilings, etched-glass friezes, terrazzo floors and subtly recessed lighting designs. Taste and Tradition
While all that is new, the Rainbow Room regains the full figure of its former self.
From the maple and fumed-oak mosaic in the middle of the dance floor, the room radiates into dining terraces and, then, in an upward sweep of floor-to-ceiling mirror and glass, seems to draw in all the lights of New York at night. The Empire State Building, to the south, looms like an outsider peering through the window.
Little of that has changed over the decades, even through a previous remodeling during the 1950's. But everything has been primped and polished to perfection.
''Layers of old fabric have been stripped from the walls,'' said Peter Spiegel, site manager for the project's contractor, the Tishman Corporation. ''Now the walls are covered with Italian silk in aubergine'' -an almost irridescent shade of deep, purplish brown.
The windows have been draped with ''scalloped Austrian blinds,'' Mr. Spiegel said, to be lowered when the weather is too moody for the festivities inside.
Every crystal from the three French chandeliers - the main one in the dome over the dance floor and its counterparts in the northeast and southeast corners - has been cleaned, polished or replaced.
The 300 color lights in the dome -which would flicker or fade in concert with the music, giving the room its name - have been rewired to synchronize with the sound system.
And the dance floor has been replaced in what has been, especially for Roger Berk, an exercise steeped in tradition.
''In the 30's,'' Mr. Berk said, ''the original installation was done by my grandfather. And then, early in the 1950's, my father replaced the floor.''
In that incarnation, however, the pattern was modified.
''What we've done now is restored the pattern of 1934,'' Mr. Berk said. ''It's a compass rose, sort of a star, surrounded by two sets of diamond patterns, each within a circular band.''
Mr. Berk admitted being ''sentimentally attached'' to a job that was ''literally in the footsteps of my father and his father.'' The Duke and Hollywood
Footsteps of dancers echo in the memories of 77-year-old Sy Oliver, the latest in a long line of conductors at the Rainbow Room - among them Ray Noble, Glen Gray, Duke Ellington, Woody Herman, Si Zentner, Russ Morgan and Bobby Rosengarden.
''The whole time I was there,'' Mr. Oliver said, ''it felt like a reward for all the years I've put in this business.
''When you're traveling all over,'' he explained, ''there are a lot places that aren't quite as upscale. I always thought of the Rainbow Room as a Hollywood set-designer's idea of what a supper club should be.'' Indeed. Gloria Swanson, Jeanette McDonald and Jean Harlow were all part of the scene.
Joan Crawford and Franchot Tone spent part of their honeymoon there. Elizabeth Taylor and Richard Burton fox-trotted under the chandelier -once called ''one of Sophie Tucker's earrings.'' Senator Jacob K. Javits and Zero Mostel danced the hora together there after the opening of ''Fiddler on the Roof.''
Of course, the not-quite-so-famous have made appearances.
In a 1965 interview, the former Brenda Frazier Kelly, the most glamorous and publicized debutante of the 1938 season, recalled, ''It was the one place we were all allowed to go.''
''That entire period,'' she said, ''is a whirlwind in my mind. Mummy allowed me to go to the Rainbow Room, but I do remember that there were some places I wasn't allowed to go. Mummy felt I shouldn't go to the Morocco after I came out. Of course, she may have had a point there.''
And one night in June 1977, like so many before and since, the senior boys from Tottenville High School on Staten Island in their beige and blue and white tuxedos, and the girls, in pink and white and yellow gowns -some even wearing gloves - actually touched while dancing to Mr. Oliver's rendition of ''As Time Goes By.''
Photo of the Rainbow Room as it originally appeared; Paul Draper (NYT/Star Black)
