The federal government says it will not give a private firm construction money for a proposed rail link between Tysons Corner and Dulles International Airport, but the company and local officials say that hopes for train service in the corridor haven't been derailed.

No one in government or the private sector has formally asked for such money, and it is not clear how much would be needed or when it would be sought, officials said yesterday.

Last week, Brian Clymer, chief of the Urban Mass Transportation Administration, wrote to a Northern Virginia attorney for the Dartrail firm and some Dulles corridor land owners that the agency does not provide rail construction money to private companies, according to an administration spokesman.

Fairfax County may seek such funds eventually, though officials there are not sure how essential they would be to their plans. It also is unclear whether the federal agency would have any money or favor the Dulles corridor over the Metrorail system.

An aide to Fairfax County Board Chairman Audrey Moore said federal construction money is likely to be "a small component" of any county-supported rail system.

Fairfax and Dartrail are developing proposals to state officials for mass transit in the Dulles corridor. In each case, a temporary bus system would be established and would later be replaced by the rail system connecting Dulles with the West Falls Church Metro station. Dartrail wants to begin rail service several years earlier than would the county.

The federal agency spokesman said the letter had no bearing on the status of Fairfax County's application for a $36 million grant to start an express bus system in the corridor. That system could eventually be converted to rail service if significant additional money is found.

State officials have pledged part of the Dulles Toll Road's profits to bus and rail service in the corridor, but they still are studying suggestions from Dartrail, Fairfax and others as to what should be done.

Virginia Transportation Secretary John G. Milliken said yesterday the federal agency's letter to attorney Curtis Coward probably won't affect the planning process. "We haven't gotten to the stage" of deciding how to fund whatever transit plans will be devised, he said.

"It's a non-event," Coward said yesterday of the letter.

Fairfax officials hope to start express bus service in 1994. The $36 million federal bus grant would be matched with local bond money. Dartrail has proposed one or more special tax districts to help finance its plans.