Bills to complete the renovation of Union Station and to extend the life of the Pennsylvania Avenue Development Corp. were caught in a legislative logjam last night as Congress plodded toward adjournment.

Without passage of the Union Station measure, the ultimate fate of its partially completed multi-million dollar transformation into the National Visitors Center and transportation terminal remains in doubt, at least until next year.

Failure to pass the Pennsylvania Avenue measure could slow reconstruction of Washington's major ceremonial boulevard, an official of the redevelopment corporation said. But he added that its day-to-day operations are not yeat in peril.

Most key legislation affecting the nation's capital in the expiring Congress had been enacted earlier.

On Friday evening, the House approved a conference report on a bill granting $1.6 billion federal subsidy over 25 years to the unfunded pension programs of the D.C. government, saving the city from a possible future threat of bankruptcy. The Senate meantime gave final approval to a bill strenthening the city's home rule powers to enact local legislation.

Both the Union Station and the Pennsylvania Avenue bills affect projects that are being conducted by the federal rather than by the local D.C. government.

The fate of the Union Station measure was in doubt because of a disagreement between the House and the Senate over the magnitude and the cost of the project. The monumental old station has been partly converted into a National Visitor Center under Interior Department jurisdiction. Parking ramps planned as part of the project are not finished. A small railroad station has been constructed in part of the former track area behind the old building.

The Senate has voted to pump another $60 million into the project, including the construction of a new intercity bus terminal. The House Public Works and transportation committee has proposed to spend $35.7 million for a smaller-project, Minus the bus terminal.

Rep. Harold T. Johnson (D-Calif.), the House committee chairman, said he would not carry the bill to a House vote until an advance agreement could be reached with the Senate. He insisted that a delay until Congress meets again next year would not be fatal to the project.

The Pennsylvania Avenue bill, previously passed by both houses of Congress in different forms, encountered a possibly fatal objection from Rep. John Ashbrook (R-Ohio), who described the redevelopment as a costly boondoggie. Ashbrook refused to agree to a proposal, requiring unanimous consent, that a joint House Senate conference be held to work out differences. Those differences involve public works projects elsewhere in the country that the Senate tacked onto the bill.

The stalled measure would authorize continued funding of the Pennsylvania Avenue project through 1983. Through a parliamentary technicality, however, Congress recently appropriated funds for the current fiscal year, keeping the project going until next Sept. 30.

F. David Harris, acting executive director of the redevelopment corporation said the congressional inaction could delay some funding needed early next year to expedite construction of a plaza on Pennsylvania Avenue between 13th and 14th streets nw.