Federal officials announced yesterday the formation of a task force to advise the Department of Transportation on the feasibility of building a 16-mile rail line linking the West Falls Church Metro station with Dulles International Airport.

The task force, to be headed by conservative political activist Paul Weyrich, comes in the wake of a proposal by a group of investors, including the prominent Washington-based Gray and Co. public relations firm, to build a $300 million rail line. It would be financed by leasing about 600 acres of federally owned land at Dulles for private office and hotel development.

Weyrich's nine-member task force will work with a DOT consultant on the general idea of building a rail line, but will not recommend that a particular investor group be chosen to build the rail line, said Alfred DelliBovi, deputy administrator of the Urban Mass Transit Administration.

Under the Gray group's proposal and similar proposals in the past, the rail line would be built on the median strip of the Dulles Access Road.

Both the median strip and the 600 acres would have to be leased or granted to the Gray group by the Federal Aviation Administration, which owns the roadway and the 10,000-acre airport.

Federal officials have said they are intrigued by the Gray group's proposed line -- known as Dulles Access Rapid Transit, or DART -- because it would involve no federal money and would be a showcase for private financing of mass transit. The Reagan administration has proposed major cuts in mass transit financing.

Weyrich, who is president of the Free Congress Research and Education Foundation and who has criticized President Reagan for not being conservative enough, said at the task force's first meeting yesterday he wants it to be "action-oriented."

"I do not like endless studies," said Weyrich, a former Senate staff member specializing in transit matters. "We need studies that lead to action, if action is appropriate."

DART, the only current proposal for a Dulles rail plan, is also the name of the company proposing the rail line. It consists of four partners, each owning one-fourth of the company, said Carl Blake, a Washington investment banker acting as a spokesman for DART. The partners are Gray and Co., whose chairman is Republican insider Robert K. Gray; Alejandro Orfila, the former Organization of American States secretary-general who recently left Gray and Co.; and Dulles area developers Bahman Batmanghelidj and Joseph Walker, Blake said.

Until Orfila's departure from Gray and Co., the firm owned half of DART, and Batmanghelidj and Walker each owned one-quarter, Blake said. But Blake said Gray and Co. transferred half of its 50 percent interest to Orfila when he left the firm, Blake said. He said he did not know the details of the transaction, and other principals involved have declined comment.

The task force's members, including business executives, a lawyer and some transit experts, were named by UMTA Administrator Ralph Stanley, Rep. Frank R. Wolf (R-Va.), Fairfax Board of Supervisors Chairman John Herrity and Loudoun County Administrator Philip Bolen.