Washington is about to get its version of Baltimore's highly popular Harborplace and Boston's Faneuil Hall wrapped into the 82-year-old Post Office Building on Pennsylvania Avenue.

The General Services Administration this week hired the architectural firm of Benjamin Thompson & Associates of Cambridge, Mass., the same firm that designed the facilities in Baltimore and Boston, to transform the long dormant Post Office Building into a center for tourist activity as well as a prestige office address for federal bureaucrats.

GSA, the government's landlord agency, said the Thompson firm and the Evans Development Co., a shopping center management firm from Baltimore, in the coming year will convert the bottom three levels of the 10-story building at 12th Street and Pennsylvania Avenue NW into a commercial mall to be called The Pavilion.

Located at the bottom of a soaring atrium topped by a bronze-tinted skylight, The Pavilion will house restaurants, snack stands, shops and entertainment facilities. Upper floors of the building will house government offices.

Not only that, but the structure's 315-foot-tall clock tower will house a set of bells that were cast in the same foundry as -- and are replicas of -- those in Westminster Abbey in London. They were a Bicentennial gift to the United States in 1976 from the Ditchley Foundation of Great Britain.

The Evans-Thompson venture won out in negotiations over the second-ranked applicant, the Rouse Co. of Columbia, the developer of both Faneuil Hall and Harborplace, according to GSA spokesman Mike Ziskind. Key figures in the Evans firm once worked for Rouse.

Joint private commercial and government use of the old Post Office Building is the first in Washington undertaken under a 1976 law that ended the traditional near-total separation of such activities.

For years, Washington planners have complained that limiting the massive Federal Triangle -- which rims nine blocks along the south side of Pennsylvania Avenue -- to government office use has condemned it to be an area devoid of human life after dark and on weekends.

The renovated old Post Office Building is intended to introduce life into the area. The structure, crafted from Maine coastal granite, was completed in 1899 during the second administration of President Grover Cleveland.

When the Federal Triangle development was later projected under President Calvin Coolidge, it was targeted for demolition. Its Romanesque Revival architecture was regarded as out of step with the neoclassicist architecture used in every Triangle building except the already existing District Building.

Preservationists persuaded Congress in the 1970s to preserve and restore the old building. In 1977, the lawmakers authorized $18 million to do the job.

Now the building has been renovated, top to bottom, using designs commissioned by GSA and drawn by Washington architect Arthur Cotton Moore.

The marble balustrades that fence off the office corridors on the inside from the 10-story-deep atrium courtyard have been scrubbed and topped with new brass safety railings of old-fashioned design. Oak paneling has been painstakingly restored in the fifth-floor office occupied by postmasters general for 35 years until the Post Office moved to a new location nearby.

Even the antique cage-type elevators that move in wrought-iron shafts have been restored but, for fire safety reasons, have been encased in heavy glass. These developments will clear the way for occupancy of the upper stories by government offices sometime next summer, according to GSA spokesman Ziskind.

The new occupants have not been selected, he said. Before the renovation, the building was occupied chiefly by Justice Department offices, including the Washington field office of the FBI.

Patience J. O'Connor, vice president of the Evans firm, said the commercial levels of the building will be filled with restaurants and various-sized shops, some of them branches of Washington establishments and others opening in Washington for the first time. The space for these is now available as a result of the renovation, but the detailed design for them must still be drawn by the Thompson firm. They could be open a year from now.

On the lowest level of the building, one story below the Pennsylvania Avenue entrance, will be two groupings of restaurants and food booths -- one, to be called Embassy Row, featuring foreign dishes, and the other, to be called Main Street, featuring domestic dishes, including the ubiquitous hot dog. Sidewalk cafes will be located outside both the north and south entries.

The lowest level also will feature a stage where entertainment will be offered, including theater performances and puppet shows.