Amid the Washington area's deepening gasoline crisis, the Trailways bus system has announced plans to eliminate all commuter service on its increasingly crowded routes between Manasses and Washington.

The cutback, scheduled to take effect July 15, prompted immediate protests from regular passengers. "If this happens, I will have to drive, or at least car-pool, in to work," Wayne McKee, a Manassas resident who work as an electronics engineer for the Federal Communications Commission in Washington, said in an interview yesterday. "I would probably use five to six times as much gasoline as I do now."

Elimination of Trailways service from Manassas and the nearby Prince William County towns of Nokesville and Catlett would leave Manassas area commuters without any direct bus transportation to the District of Columbia, officials said.

The announcement of the planned halt in bus service led yesterday to an investigation by the Interstate Commerce Commission. ICC officials said they would decide by Friday whether to seek a federal court injunction to bar the cutbacks, which would affect several hundred commuters.

Last night a spokeman at Continental Trailways headquarters in Dallas raised the possibility that Trailways may already have started backing away from its threatened halt in Manassas service. The spokeman quoted Trailways senior vice president Ted Knappen as saying the announcement was only a "first step" that "does not necessarily mean" service will be eliminated.

The Colonial Transit Co. currently provides commuter services between Manassas and the Pentagon, according to Colonial president Gary Penn. Colonial has recently been plagued by equipment breakdowns and maintenance problems.

Manassas commuters could switch at the Pentagon from Colonial buses to the Metro system. There is no Metrobus service to Manasses. The nearest Metrobus stop is at Greenbriar northwest of Fairfax City, according to a Metro spokesman.

Last year, the Interstate Commerce Commission obtained a temporary restraining order to block more limited reductions in the Manassas-to-Washington service by Trailways.

Robert W. Waldron, operations manager of the regional ICC office in Philadelphia, said yesterday his office has received numerous complaints from Prince William County commuters. "Some of (the Manassas passengers) would have no transportation (to Washington) at all."

The Virginia Corporation Commission may also schedule a hearing on the planned Trailways move if the commission receives protests from passengers, officials said yesterday.

"It's unfortunate that the issuance of the bulletin (announcing the cutbacks) coincided with the energy crunch," a Trailways spokesman in Washington said yesterday. "Our position is simply that the operation has been extremely costly. We have never managed in recent years to even break even on it."

The spokesman attributed Trailways' financial troubles on the Manassas routes to rising fuel and labor costs as well as the problem of deadheading. Deadheading, a widespread difficulty in the transit industry, is the practice of dispatching empty buses to a location, such as Manassas, where they can pick up commuters and begin a return trip. Bus operators collect revenue only on the return trip but incur labor, fuel and other expenses on both trips.

Trailways senior vice president Knappen plans to schedule a meeting with Manassas commuters to discuss fare increases for the money-losing possible government subsidies and Manassas-to-Washington lines, the spokesman said.

Some Manassas commuters had already predicted such a move. "I just think this is the first play in the ball game," said Maria Phillips, a Commerce Department employe who commutes from Manassas. Her forecast, she said, is that Trailways will end up with a slight reduction in service to Manassas and a large fare boost.