Harry Weese, the Chicago architect who designed Washington's Metrorail stations, has won the competitiion for a new master plan to bring the Federal Triangle to life and to reconcile the ugly clash between its neo-classic buildings and the romanesque Old Post Office.

Weese's selection from among three finalists will be announced this morning by Jay Solomon, administrator of the General Services Administration, which is in charge of all federal office buildings.

Under the Weese plan, the Old Post Office, now being recycled intoa unique office building and tourist attraction, is to be surrounded by lively plazas and arcades for outdoor festivities and ceremonies -- the city's front porch, as it were, where we greet the tourists on the Mall.

Solomon readily agreed with the Fine Arts Commission which urged last year that the Old Post Office not be restored in isolation but be given a pleasant and lively setting.

With its 350-foot tower, it has been a massive, granite thorn in the more delicate architectural tissue of the Federal Triangle. The Triangle architects assumed that the older building would be torn down. They built their New Post Office and Internal Revenue Service building on either side of 12th Street -- grand courts and all -- right up to the romanesque granite pile.

The Depression saved the pile, but left it without life and dignity amidst the brick-bandaged stumps of the Triangle buildings. The half-completed courts became parking lots.

Weese's cure for the stumps (also suggested by another finalist, a team headed by architects Sert, Jackson and Associates), is a breakthrough in contemporary architecture. Weese would cover the stumps with exact replicas of Federal Triangle porches and facades. A few years ago Weese and other modern architects would have felt compelled to do something "modern" and awful. (The third finalist team headed by landscape architect Hideo Sasaki proposed just that."

More impressive even than Weese's architectural solution is his urbanistic one.

By reducing 12th Street to three northbound automobile lanes, removing curbs and adding bollards, he would pull the awkward hemicycle in front of the New Post Office toward the old one. Adorned with spouting water jets and textured paving, this would create a plaza similar to the one between the National Art Gallery and I. M. Pei's East Building. It would become a wide-open invitation for the tourists on the Mall to venture toward the city.

The small court east of the old Post-Office would become a more intimate urban space with a pond (for ice skating?), lined to the south by the IRS building's arcades. They would shelter "culinary embassies," restaurants of different nationalities. Under this space would be a parking garage. A narrow passage would link it to Pennsylvania Avenue.

Weese would also provide more entrances into the Old Post Office and link his complex to the rest of the Federal Triangle by a walkway leading through its buildings and courts.

The plan will now have to run the gamut of commission approvals, environmental impact statements and all the rest. It should be ready for submission to Congress in July 1980. The cost is about $17 million. The Old Post Office remodeling is scheduled to be completed in March 1981.