The opening of two new Metrorail segments -- the Yellow Line between Gallery Place and National Airport and the Blue Line extension to Huntington from the airport--seems certain to be delayed at least until February 1983 and probably later, Metro officials said yesterday.

The track was supposed to go into service in December of this year.

Metro blames a strike in a factory near Pittsburgh. It was making brake systems crucial to production of 50 rail cars needed to open the new track. The strike is now 3 1/2 months old. Labor and management are negotiating under federal mediation.

Without the parts that lie unfinished in the Pittsburgh plant, Breda Costruzioni Ferroviarie of Italy cannot complete four prototype rail cars, test them and begin regular production. The U.S. factory also has a contract to supply Breda with brakes for the production cars.

More than 150 nonunion employes are working in the U.S. plant, which is owned by Westinghouse Air Brake Division, part of the conglomerate American Standard Inc. However, Metro officials said it was unclear whether this slim work force--over 2,500 people are normally employed in the plant--could complete the parts for the prototype cars.

Metro General Manager Richard Page said that by reducing service on subway lines already in operation, Metro could open parts of the new Blue and Yellow track without the Italian cars. But he said he would not recommend that, because the rail car fleet is already spread thin. That decision is up to the Metro board.

Metro already took cars off the Blue and Orange lines to open three new Red Line stations in December without expanding its fleet. Then came last month's accident under the Mall, which killed three passengers. That accident put two cars out of service, leaving a total of 298.

Metro officials said the complexity of producing brake systems makes it impractical to transfer the contract from Westinghouse. Moreover, with strikes considered a legitimate excuse for late delivery, there would be legal difficulties in switching contractors.

Before Breda was awarded its contract--it will make close to 300 cars for the Washington rail system over five years--Metro officials visiting Italy met with leaders of its unions to seek assurances that strikes would not disrupt production. Now they find the problem has emerged in the United States instead.

Opening of Yellow Line service will mark Metrorail's second river crossing. Trains will run from Gallery Place, pass under the Mall and the Washington Channel, surface on Hains Point, cross the Potomac on their own bridge at 14th Street, then link up with Blue track at the Pentagon and go on to National Airport.

Blue Line trains, meanwhile, will begin running south from the airport to Huntington. That will bring the first Metrorail service to Alexandria, redraw commuting patterns for many northern Virginians and make Blue the first of the five color-coded lines in the rail system's 101-mile master plan to be completed.

The two segments will add 8 1/2 miles of track and five stations to the 39 miles and 43 stations now in service.

After that, the next segment to open will be 14 new miles of Red Line track to Shady Grove. That is scheduled for late 1983.

Funding is assured for those segments, but the future of 40 miles remaining after that is in question due to federal budget cuts.