The outlook for the U.S. Postal Service's controversial plan to renovate and expand the old city post office near Union Station became murkier this week as legislation was introduced in Congress to allow it to take over the building for its own use.

Sen. Wendell H. Ford (D-Ky.), chairman of the Senate Rules and Administration Committee, sponsored the bill to transfer ownership of the massive structure at Massachusetts Avenue and North Capitol Street NE from the Postal Service to Congress for use as congressional offices, a printing plant, warehouse and a truck delivery facility.

The legislation could signal the end to the Postal Service's proposed $100 million renovation of the historic facility, a plan that has been opposed as overly aggressive by historic preservationists. But city officials, trying to push development of the Union Station area, have warmly embraced the redevelopment plan throughout the heated debate during the past year.

Last month, the National Capital Planning Commission, the central planning agency for the federal government in the Washington area, overwhelmingly rejected the Postal Service's proposal to turn the city's former central mail handling facility into a large complex of offices and shops. At the heart of the denial was the NCPC's opposition to the Postal Service's attempt to add 1 1/2 stories to the structure.

Spurred on by the NCPC vote, seven congressional committees, led by Ford's Senate Rules Committee and Rep. Frank Annunzio's (D-Ill.) House Administration Committee, have been investigating ways to obtain the building for Congress. For the past several years, Ford and others have been pressing to get more space to alleviate what they say are overcrowded conditions on Capitol Hill.

Postal officials and their private New York development partners still hope to develop the site, although they acknowledge Ford's bill has created a major roadblock.

"We hope to convince Congress that {its use} of the building would not be appropriate," said Stephen Porter, an attorney for the project's private partners, a group that includes two large New York development firms.

Asked if his clients were preparing to abandon their proposal, Porter said, "There's no possibility that the developers will walk away from this project. If taken by Congress, then the project got pulled away from us."

Porter said it is now up to the Postal Service to handle negotiations with Congress for control of the structure. "It's their building," he said.

Dennis Wamsley, real estate manager at the Postal Service, said his agency had "no formal response" to Ford's bill. But he said the Postal Service has no "institutional objection" to Congress obtaining the building providing the agency receives "due compensation."

The Ford bill makes no mention of a specific purchase price for the 73-year-old Beaux Arts building. It said a price will be negotiated between Postmaster General Preston R. Tisch and 10 members of Congress.

Funding for the building's acquisition for Congress could be a sticky issue given the current political liabilities associated with increasing the federal budget deficit.

The bill does not clearly state whether Congress will propose to add on to the roof, which is opposed by preservationists and the NCPC, both of which argue that the structure's architectural character would be destroyed by such alterations.

Instead, the legislation states that Congress, in restoring the building, will "recognize" and "retain" the building's original appearance "to the maximum extent feasible."

It is also unclear whether the congressional committees involved in the effort to obtain the building are merely using the bill as a means to increase their bargaining position with the Postal Service to obtain space in the building should development of the site proceed.

Congressional committee staff members this week said they plan to continue talks with postal officials over the future of the building, leaving open the possibility that development of the site might still occur.

Hearings on the legislation have not been scheduled.

The building has sat mostly empty since the Postal Service moved the city's main mail-handling operations to Brentwood Avenue NE last year.

In addition to opposing the plan to increase the height of the landmark building by 33 feet, opponents of the Postal Service's proposal also charged that the increased size would worsen traffic congestion in the Union Station area.

The additional 1 1/2 stories would have created 350,000 square feet of new office space, an amount larger than nearly any new downtown office building.