Senior Metro officials raised doubts yesterday that 8.5 miles of Yellow and Blue line track, linking Gallery Place downtown and Huntington south of Alexandria, will open on schedule in late 1982.

Assistant General Manager John Egbert told the Metro board that a strike at a Pittsburgh factory making railcar brakes could delay delivery of 50 or more cars needed to open the new track. But he said that even if the cars arrive on schedule, Metro may not finish its own tests in time.

"A December opening to Huntington is an optimistic" schedule, said Metro's general manager, Richard Page.

The cars' manufacturer, Breda Costruzioni Ferroviarie of Italy, needs brake components from the Westinghouse Air Brake Division, part of the equipment conglomerate of American Standard Inc., for four prototype Metro railcars. Assembly of the parts has been suspended by the strike, Metro officials said.

The strike began Nov. 1. If it continues for two or three weeks longer, Egbert said, it could push back delivery of the cars to Metro, now scheduled for June of next year.

Metro's board chairman, Joseph Alexander, asked his staff to investigate what legal action Metro could take to end the blockage of delivery schedules.

After the Red Line is extended through to Van Ness this weekend, the new Blue and Yellow track is next in line to open. That extension would bring the completed subway system to just below half of its full design length of 101 miles, and would open the first rail service in Alexandria.

The new track includes seven stations. Service would not be direct from Gallery Place to Huntington; in effect, the Yellow Line would function as a shuttle across the Potomac River by bridge, enabling passengers to transfer to the Blue Line in Virginia.

In other action yesterday, the board:

* Gave final approval for special minibus service between Georgetown and the Kennedy Center to begin on Dec. 13, with flat fares of 50 cents. Minibus service is scheduled to begin on three other routes on Jan. 31.

* Approved experimental alterations in two bus routes in Fairfax. The 5K bus will begin serving the Lewinsville retirement homes on Great Falls Street in McLean. The 5S will be rerouted to serve the Hunters Woods area of Reston.

* Approved a retirement package for Page. Each year, he will receive deferred compensation of 10 percent of his annual salary, which presently is $73,000. On leaving his job, he also will receive $25,000 for his service to date, provided that he stays at least three more years.