A $112 million office, hotel and apartment project planned on Pennsylvania Avenue across from the National Gallery of Art got an official go-ahead yesterday from the Pennsylvania Avenue Development Corporation, which is overseeing reconstruction of the nation's foremost ceremonial boulevard.

PADC directors also approved the construction of a handshell and stage, large enough for a full symphony orchestra, in Market Square Park opposite the National Archives. The project will be a memorial to all persons who have served in the Navy, and will be erected at a cost estimated at between $5 million and $10 million by the Navy Memorial Foundation.

The office, hotel and condominium apartment project -- the costliest development to date along the historic mile-long stretch of the Avenue between the Capital and the White House -- was proposed by the Westminister Investing Corp., a subsidiary of the B. F. Saul Co., a major old-line Washington realty firm.

It will occupy most of the eastern end of the two-block area extending northward from Pennsylvania Avenue to Indiana Avenue between Sixth and Seventh streets NW, facing both the National Gallery on Constitution Avenue and the Federal Trade Commission directly across Pennsylvania Avenue.The Saul interests own 55 percent of the privately owned land that will form the building site. The biggest structure now on the site is the Central Union Mission, 613 C St. NW, an overnight accommodation for homeless men, which is expected to move to another location.

Because acquisition of some private landholdings, including the mission, is needed to fill out the site and that of the adjacent Apex Building reconstruction at Seventh Street and Pennsylvania Avenue, the PADC board voted to authorize the use of its condemnation powers if the developers' negotiations fail. Once acquired by PADC, the land will be sold or leased to the developers.

PADC approval for both the Saul and Apex projects was preliminary. That means planning for the projects can proceed, but the developers must return when they complete their final plans.

The Saul project will include an office building fronting on Pennsylvania Avenue, which will have a facade similar to that of the Metropolitan Hotel, which stood on the site in the 19th Century. It also will incorporate the existing facade of the Old Atlantic Coast Line Railroad ticket office building at Sixth and Pennsylvania.

To the north, on sections of the site that will require the closing of C Street and narrowing of Indiana Avenue, will be a hotel with 300 to 350 rooms -- including some suites for permanent guests -- and an unspecified number of condominium housing units, possibly around 250.

The Navy Memorial bandstand will incorporate a water display and sculpture and will be available for outdoor concerts by the Navy Band and other service bands, as well as the National Symphony Orchestra. Its precise location and design have not yet been decided.