The District of Columbia's landmarks board has voted to make much of Washington's old downtown a historic district--an action which, if embraced by the Barry administration, would preserve dozens of the city's oldest commercial and residential buildings.

The decision, announced yesterday, is the latest move in a high-stakes dispute that pits developers against preservationists in much of the city's old retail core along F Street and lower Seventh Street NW. Just two weeks ago, Mayor Marion Barry's Downtown Committee, composed chiefly of business leaders and city officials, recommended that the area be redeveloped as primarily a business and office area.

As approved Monday in closed session by the Joint Committee on Landmarks, the new historic district extends along Seventh Street from Pennsylvania Avenue to Mount Vernon Square, near K Street, and along F Street from Seventh to 11th Streets, and includes some side streets as well.

If the district is accepted by Robert L. Moore, Barry's housing director and historic preservation officer, buildings within the boundaries could not be demolished or significantly altered without a review and permission from the committee.

The district is smaller than that proposed last year by Don't Tear It Down, a preservationist group that sought to extend it westward on F Street almost as far as the Treasury Department at 15th Street.

In its action, the committee also consolidated two separate but overlapping districts that had been proposed by the group for preservation--the Chinatown area, centering on Seventh and H streets NW, which was a residential neighborhood in the city's early decades, and the downtown area, where many existing building date from roughly the Civil War period of the 1860s.

David Bonderman, the lawyer who represented Don't Tear It Down at hearings early this year, said he had not read the decision and would not comment beyond praising the panel for "acting forthrightly."

Whayne S. Quin, who represented landowners opposed to the proposal, said it will be studied for a possible legal challenge. He said the landowners will file statements of opposition when Moore, as required, seeks public comments before making his final decision.

Msgr. E. Robert Arthur, pastor of St. Patrick's Catholic Church, voiced strong disappointment, saying any move that would block the 192-year-old parish from redeveloping substandard commercial buildings it owns in the 900 block of F Street would imperil church finances and threaten closure of its girls' academy.

"I suspect he Moore is going to sit on it until after the election, anyway," Arthur said.

Barry, Moore's boss, is looking to the business community for support in his bid for reelection.

Among structures in the historic district are the main and north buildings of Woodward & Lothrop and the F Street wing of Hecht's department store.