John Hart "Jack" Duvall, 66, an entertainment lawyer who commanded his own stage presence as a member of a singing group that performed at the annual spring Gridiron Club dinner lampooning Washington politicians, died of cancer Aug. 2 at his home in Alexandria.

Mr. Duvall had specialized in entertainment law since 1979 and did contractual work for his brother, the movie and stage actor Robert Duvall.

John Duvall, who had studied voice privately since he was a teenager, was elected to the Gridiron Club in 1964 as featured singer, doing political parodies of popular classics and operatic arias.

The club, made up of 60 active print journalists and 75 who are retired, brought in Mr. Duvall and 10 others for their singing ability. They were made "limited members" and performed over 35 years to an audience that included seven presidents, from Lyndon B. Johnson to President Clinton.

As the senior tenor in the group, Mr. Duvall led the white-tie sessions in the event's traditional closing of "Auld Lang Syne." At the most recent Gridiron dinner in March, he performed in a wheelchair because of his illness.

A son of a Navy admiral, he was born in Annapolis and grew up on Navy posts. He graduated from Principia College in St. Louis and then George Washington University law school in 1960. He postponed practicing law to join a GWU singing group that traveled across the nation. His experience under the stage lights included a summer at Radio City Music Hall in New York, where he was booked for seven shows a day.

He returned to the Washington area in 1962 and spent the next 17 years with an Alexandria law firm that eventually became Schonberger, Billowitz & Duvall.

He opened a solo practice in 1979. As a trial lawyer, he was primarily involved in child custody hearings. But he also counseled local entertainers on contracts and represented his celebrity brother on movie deals.

Mr. Duvall produced, wrote and starred in parodies for gatherings of the Alexandria Bar Association.

He also was a board member and first reader of First Church of Christ Scientist in Alexandria.

In addition to his brother, survivors include his wife of 39 years, Yvonne Emmons Duvall of Alexandria; a daughter, Ashley Elizabeth Hayes of Liverpool, N.Y.; and another brother, William Duvall Jr. of Milwaukee.