Top Department of Transportation officials enthusiastically endorsed yesterday a consultant's proposal for private development of a $143 million, high-speed passenger rail line that would link the Metro system to Dulles International Airport.

A DOT task force is expected to adopt the major provisions of the proposal next week. It calls for using a novel financing method that would raise the bulk of its costs through increased taxes on properties near the line, by charging passengers at National and Dulles a special fee and by raising tolls on the Dulles Toll Road.

The plan has drawn strong support from Reagan administration officials because it would require no federal funds to build or to operate the service. The administration has cut funding for mass transit for several years, and officials say the Dulles proposal is a textbook example of how private funds can provide public transit.

"This project can be a national model," said Ralph L. Stanley, head of the Urban Mass Transportation Administration, which assembled the task force. "The conclusion here is that it's entirely feasible to build a light rail system to Dulles exclusively with private funds."

Some Northern Virginia officials questioned the feasibility of the plan, saying they don't want local taxpayers to have to carry the burden of a new 16-mile rail line that would run mostly in the median strip of the federally owned Dulles Access Road.

"I don't want to be a wet blanket," said Fairfax County board Chairman John F. Herrity. "But where is all this money going to come from?"

The proposal calls for the system to stop at six stations between Dulles and West Falls Church, where an Orange Line Metro station is scheduled to open next summer. Each station would operate on a fare card system and would have parking spaces for up to 600 automobiles. Travel time between Dulles and West Falls Church would be 21 minutes. The report estimates that 17,000 people would ride the system each day by the year 2000.

Only 15 percent of the riders are expected to be taking trips to or from the airport; most would be commuters, according to the study. It said most rides would cost $1.50. Trips to the airport from West Falls Church would cost $3.50.

Several groups of investors have expressed interest in building a rail line to Dulles, but officials say the most sophisticated proposals have come from a venture called Dulles Access Rapid Transit, or DART. Its chairman is Najeeb Halaby, adminstrator of the Federal Aviation Adminsitration in the early 1960s, and a former airline executive. Other DART investors include Alan Boyd, a secretary of transportation under President Johnson, and William T. Coleman Jr., secretary of transportation for President Ford.

Until recently the Washington lobbying firm, Gray and Co., whose chairman is Republican insider Robert K. Gray, owned 25 percent of the rail company.

"Rail transit has not really been financed privately for well over 50 years in this country," said C. Kenneth Orski, president of Urban Mobility Corp., a transportation consulting firm. "It could work, it's within the realm of possibility now. But the biggest question is how much real estate investment could the new line stimulate?"

Financing remains the biggest obstacle. As the Reagan administration has reduced subsidies to railroads, mass transit proponents have sought to finance rails by taxing properties near the line's stations. The idea is that the properties along the line rise in value because of the new rail line.

That is one of the major ways that the study proposes to fund the Dulles line. While administration officials endorse this aspect of the proposal, many Virginia officials are skeptical because it would require special legislation from the Virginia General Assembly and the legislature is reluctant to give localities more taxing powers.

Fairfax officials also are concerned about the prospect of increased development along the route of the proposed rail line. While the county supervisors have made development of the Dulles area a top priority, they also want to keep part of that corridor zoned for low-density development.

"We are not going to allow Fairfax County to become a concrete jungle for anybody," said Herrity. He and other supervisors have made clear that they are opposed to altering the county's master plan for development because of the rail proposal.

The chairman of the task force, conservative activist Paul Weyrich, said yesterday that he believed the concern of Fairfax officials could be accommodated.