The Truxtun-Decatur Naval Museum, which once served as stables to Decatur House, the landmark 1819 building on Lafayette Square, will be remodeled into a conference, exhibit and reception space, according to Michael Ainslie, head of the National Trust for Historic Preservation. A $500,000 donation from Edith Munson, a former golf champion and American Red Cross official, will pay for the renovation.

The Truxtun-Decatur Museum has occupied the building at 1610 H Street, a block from the White House, since 1949. Its collections will be merged with those of the Navy Memorial Museum in the Naval Yard, according to Adm. John Kane, vice president of the Naval Historical Foundation, which founded Truxtun-Decatur in the 1920s. The renovated Navy Museum, with the addition of the 500-odd artifacts from Truxtun-Decatur, will reopen Dec. 7, at the same time the Truxton-Decatur closes for renovations.

Decatur House was designed by Benjamin Latrobe, the first professional architect in the United States. It was the first and last private house on the President's Park, later Lafayette Square. Stephen Decatur, a Naval hero who tamed the Barbary pirates, built the house and moved in by 1819. Decatur was killed in a duel about 18 months later.

The house was later occupied by the French, Russian and British ministers, three secretaries of state (Henry Clay, Martin Van Buren, and Edward Livingston), John Gadsby (of the Tavern), Vice President George Dallas (for whom the Texas city was named), a secretary of the Treasury, assorted senators and congressmen, and Gen. (later Ambassador to Austria-Hungary) Edward Fitzgerald Beale and his wife Mary Beale.

The house remained a private residence, a center of diplomatic and political entertaining until the death of Marie (Mrs. Truxton) Beale, the general's daughter-in-law, in 1957. Mrs. Beale's gaslit parties were famous because, among other reasons, her wine cellar outlasted Prohibition.

Latrobe also was the architect of St. John's Church on Lafayette Square, and an architect of the Capitol. He made alterations to the White House and built 12 or so houses in Washington. But Decatur House is the only one to survive.

The new use for the old building follows a recent study of Decatur House and its dependencies by architect Francis Donald Lethbridge. Lethbridge suggested that the new facility, with kitchen and toilets, be used to take some of the burden off Decatur House. According to trust architect Richard Bierce, the principal part of the old stable, 70 feet long, 25 feet wide and 12 feet high, will be a ballroom-for-hire. A greenhouse link to the present garden, redesigned in the early '70s by Dudley Brown, may also be included in the remodeling.

The stables themselves may not have been designed by Latrobe and may have been built later than the house, Lethbridge said. After the house was occupied during the Civil War, the owner filed a damage claim citing the demolition of the stables by the government.

Gen. Beale had what were called the largest and finest stables in Washington, so it is possible that the bulk of the stable construction dates from his 1874-1893 residency. A garage was added to the structure for Marie Beale's car when the stables became a museum.

"When we remodel the building, we hope to find out just what remains of the original structure," Bierce said.