A group of private investors said yesterday it is prepared to build at its expense a 75,000-seat domed stadium near Dulles International Airport in the event of unsuccessful negotiations between Washington Redskins owner Jack Kent Cooke and the D.C. government to keep the team in the District.

Other Northern Virginia developers expressed strong doubts over whether a stadium complex near the airport in Loudoun County is feasible.

Members of Ultra-Dome Consortium, a group of Washington area real estate investors, said it has plans for a $770 million complex in Loudoun, featuring a multi-use stadium surrounded by a shopping mall, a luxury hotel and a convention center. The investors said the stadium development would include a stop on a proposed commuter rail line to Dulles.

However, other experienced Northern Virginia developers cited the cost of the project, the remote prospects for a commuter railway and the county's location -- 25 miles from downtown Washington -- as major problems for a Loudoun stadium.

"The Loudoun idea is very far-fetched," said Robert Buchanan, a prominent developer along Loudoun's booming Rte. 28 corridor. He said he sees the proposal as a ploy by Cooke to pressure the District government during stadium negotiations.

"I'd hate to consider us as a pawn in a game; I can't honestly say it's not being done," said developer Marilyn DeLuca, who with her husband Robert DeLuca is one of the organizers of Ultra-Dome. "I would hope the Cookes would not use us as pressure on the District."

The stadium complex would be built without public money, and the 10 members of the consortium say they believe that they are wealthy enough that they would have no trouble financing the project, said Marilyn DeLuca.

"There's been substantial interest" among investors, she said. "There's no problem with the funding."

DeLuca said the Ultra-Dome group is not trying to lure the Redskins from the District, only to be an alternative if negotiations to use public money to build a domed stadium in D.C. fail.

"I don't think we would proceed any further until Mr. Cooke indicated a positive {interest} toward relocating the Redskins in the suburbs," DeLuca said.

Cooke did not return telephone calls.

Cooke and D.C. Mayor Marion Barry have been engaged in recent months in a high-profile game of public jousting and private bargaining over Cooke's hopes to replace at public expense the 55,000-seat RFK Stadium. Cooke has complained that RFK is too small, lacks lucrative sky boxes and is poorly suited to professional football. He has expressed a preference for a domed facility that could be used to land a Super Bowl game for Washington.

Last week Cooke issued an ultimatum, giving the District until June 30 to come up with a new stadium proposal to keep him from pursuing alternatives in the suburbs.

The possibility of a Loudoun stadium has been floating publicly since October. Wendell Johnson, a Fairfax County architect and designer, said yesterday the notion of using a stadium as the anchor for a much larger convention, office and retail development first came to him in the fall.

Johnson said he took the idea to Steve W. Stockman, a Republican member of the Loudoun County Board of Supervisors, who arranged a meeting with the DeLucas, who are well known in Northern Virginia development circles. The Ultra-Dome Consortium evolved from that meeting, participants said.

Stockman said he has served as "a facilitator" in Ultra-Dome's stadium discussions.

Johnson said members of the Redskins organization, including Cooke's son, John Kent Cooke, have expressed interest in Ultra-Dome's proposal, some details of which were disclosed in yesterday's Washington Times.

A site for the 350-acre development has not been purchased, but two locations are being considered and a third is being looked at as a fallback, DeLuca said. All the locations are next to Dulles, where land sells for as much as $2 a square foot.

Ultra-Dome's proposal makes sense because football stadiums by themselves lose money, according to Johnson and DeLuca. A stadium used for football and also for circuses, tractor pulls and other events as many as 180 days a year could be profitable, particularly as the hub of a development, DeLuca said.

In addition to the shopping mall, hotel and convention center, the stadium complex would include an unspecified number of condominiums and a new practice area for the football team, which now works out at Redskins Park in nearby Herndon.

The Rte. 28 corridor, fueled by the dramatic increase in air traffic at Dulles, in recent years has become the scene of some of the most energetic land speculation and development in the Washington area.

Various ideas, involving both public and private financing, have been floated for connecting Dulles by rail with the Metrorail system. None of those plans has gathered visible momentum.

John White, a spokesman for Barry, said yesterday the administration is continuing to explore options for a new stadium, including a plan involving private investors. Staff writer John Lancaster contributed to this report.