President Carter has signed legislation authorizing expansion of the Manassas Battlefield National Park, ending a five-year battle between historic preservationists and developers.

The bill signed Monday night by the president authorizes the Interior Department to acquire an additional 1,498 acres for the Civil War battleground park in Prince William County.

Interior's National Park Service may spend up to $8.7 million to acquire the land, which history buffs contend will permit the park to encompass three major battle sites now outside the park's boundaries.

Supporters of expansion will mark the signing of the bill with a "victory at the third battle of Mansassas" party Friday night at the home of Annie Snyder, president of the Save the Batlefield Committee. Mrs. Snyder's house abuts the Brawner Farm, one of the three major parcels set for acquisition under the legislation.

Funds for the purchase of land or in some instances, acquisition of scenic easements, will come from a federal land and conservation fund, and will not require new appropriations, according to Rep. Herbert E. Harris II (D-Va.), a longtime supporter of expansion and sponsor of the original legislation. The legislation, as passed by Congress last month, was sponsored by Sen. John W. Warner (R-Va.), and reprsented a compromise from a more ambitious proposal backed by Harris.