The Fine Arts Commission yesterday held up full approval of the remodeling of the Old Post Office saying it failed to resolve a basic problem of the site.

Chairman Carter Brown said the commission approved the plan to turn the building into an innovative mix of shops, restaurants and federal offices around a 196-foot-high interior court.

But, he said, the plan did not solve what he said was the most important problem: "the truncated stumps, the bleeding amputated limbs" where the federal Triangle meets the Old Post Office.

When the adjacent Internal Revenue Service structure was built, a semi-circular wall was left unfinished in anticipation of the Old Post Office being torn down and a neo-classical building replacing it. The wall remains unfinished, and a parking lot has grown up around it.

The commission complained that the General Services Administration's post office project did not deal with the basic problem of what happens to the area of the wall and parking lot. GSA is responsible for all federal buildings.

Architect Arthur Cotton Moore, who won a competition to design the remodeling, had proposed a new public entrance where the loading docks and the parking lot are now.

Moore sees the loading dock entrance off 12th Street as attracting people in from the Mall to the planned new facilities.

"We should not approve a plan that would lock the Capitol forever to this visual blight," Brown said. "It is time we solved forever the problem of where the two (the romantic Old Post Office and the classical Federal Triangle) meet."

He praised the Moore plan for "its imaginative mixed use of the Old Post Office. We are enthusiastic about restoring the glass roof and the use of the tower. The plan is flexible and interesting. But the key is the context of the building," he said.

Brown told GSA that work could begin to restore the glass roof and to remodel the inside. "But we want to be in touch with them as they work out the new entrances. It's such a marvelous opportunity since GSA owns all the buildings in question, and Moore is such a brilliant designer. I also have a high regard for administrator (Jay) Solomon's visual taste. I'm sure it can all be worked out."

Solomon, after hearing about the Fine Arts Commission action, said "We have been aware of the 12th Street problem, and we're trying to do something about it. I have already ordered the architect to work on it.

I hope to sit down and talk with everybody tomorrow. I have respect for Carter Brown's opinions."

Moore said he told Brown "no architect ever minds having the work expanded. I think the unfinished ends of the IRS building should be resolved. That was not parat of the GSA's original program. But it should be. The worst thing to me is that big parking lot there, where 11th Street ends. It should be a grand courtyard with fountains - not a dumb parking lot. I plan to meet with Mr. Solomon about it tomorrow."

The problem of reconciling the neoclassic architecture of the Federal Triangle and the Richardson Remanesque Old Post Office has bothered architects and planners for years. The answer to many people for decades was to tear down the Old Post Office and replace it with a building to match the rest of the Triangle. A later plan would have left only the tower standing.

But in recent years, sentiment to preserve the building was aroused by Don't Tear It Down, an organization of preservationists sparked by architect John Wiebenson, and the architectual division of the National Endownment for the Fine Arts.

Moore is part of a joint architectural-engineering venture with McGaughy, Marshall and McMillan of Norfolk, Associatted Space Design of Atlanta, and Steward Daniel Hoban of Washington.

Construction was to begin this September. The projected cost is $16 million. It is not known how the commission's action will affect the cost and the starting date.

Moore's plan conceived of the Old Post Office as building a bridge between the local city and the federal capital. The plan was hailed as a bold departure for the GSA, which up to then was known for its espousal of bland architecture.

The remodeling will put a luxury restaurant and boutiques in what were the basement, first and mezzanine levels. On the second-through-ninth floors, federal offices, including the Endowments for the Arts and Humanities, would encircle the spectacular inner court or cortile.

The landmark clock tower, at Pennsylvania Avenue and 12th Street, would become an observation platform, reached by a glass elevator. On the inside, the base of the tower, revealed by cutting away the main floor, would form a stage for music and theatrical performances.

Brown added: "I think it may well be that the Carter Administration will be longest remembered for what they have done to complete Pennsylvania Avenue. Today, with the saving of the Willard Hotel, the new sculpture being commissioned, the trees and sidewalks installed, the avenue is really beginning to take Off. It is so important that this difficulty be worked out."