The people who operate rail systems in Northern Virginia and support additional public transportation were looking for Plan B yesterday, after voters soundly rejected a proposal to raise the sales tax and pour millions into transit projects.

Virginia Railway Express lost $100 million it was counting on to purchase 50 rail cars. The top manager of the fast-growing railroad said the tax defeat means that crowding will continue on trains and in parking lots and that about a year from now VRE trains won't be able to carry any additional passengers.

Metro is counting on millions of dollars from Northern Virginia and several billion from governments in Virginia, Maryland and the District over the next 10 years for maintenance of trains, buses and stations. The defeat of the half-cent-per-dollar sales tax increase could stymie Metro's plans and increases the likelihood of a fare increase next year.

But the greatest uncertainty following the election surrounds the region's biggest public works proposal: a $3.3 billion venture to extend Metrorail 24 miles from West Falls Church to Tysons Corner and Dulles International Airport.

The rail project is in the final stages of environmental review, and Virginia officials had hoped to win federal approval to begin engineering work next year. But to join the intense national competition for scarce federal funds, the Dulles rail project needs a sturdy financing plan.

If the sales tax had passed, it would have generated $350 million for Dulles rail, to help pay the local share.

Boosters of Dulles rail said its financing plan didn't rely on the sales tax increase. "Money coming in through the referendum was a bonus; it would have been a down payment," said Leo J. Schefer, president of the Washington Airports Task Force, a business group backing the rail project. "But the project was never predicated on the referendum."

Under a financing plan for Dulles rail devised by state officials before they tried to pass the transportation tax, Virginia would seek 51 percent of the capital cost -- the maximum allowed -- from the federal government. The rest of the bill would be divided among the state, paying $800 million; Fairfax and Loudoun counties, paying $514 million and $152 million respectively; and the Metropolitan Washington Airports Authority, paying $134 million. The state would raise its share from toll increases along the Dulles Toll Road, while Fairfax County would create a special tax district for property owners in Tysons Corner.

Some officials said the original financing plan may no longer be feasible as local communities face increasing budget pressures.

Katherine K. Hanley (D), chairman of the Fairfax Board of Supervisors and one of the project's champions, said the Dulles project now must compete for money with police and schools, setting up tough choices for local leaders.

Al Eisenberg, a lobbyist for the Greater Washington Board of Trade who worked to pass the transportation tax, said that local jurisdictions will have a tough time making a case for rail to Dulles. "It would be hard under this current recessionary economic environment right now to come out of local budgets," he said.

And Del. Kenneth R. Plum (D-Reston) said trying to create the special tax district in a soft economy comes with its own challenges. "A special tax district in a time of economic decline will also be difficult," he said.

Others were more blunt. "Dulles Rail will never be built," said Del. John A. "Jack" Rollison III (R-Prince William), author of the referendum legislation.

Critics of the rail plan say the tax's defeat gives them a chance to promote a much less expensive alternative, bus rapid transit. Bus rapid transit, or BRT, is a form of mass transit relatively new to the United States in which buses mimic the subway, running at high frequency in reserved lanes and stopping at stations, where passengers quickly board and debark from multiple doors.

"The financing for rail has collapsed," said Thomson Hirst, a Reston commercial office developer who wants the state to create BRT in the Dulles Corridor.

Bill Vincent of the Breakthrough Technology Institute, a Washington-based nonprofit group that promotes new environmental and energy technologies and has been pushing BRT for the Dulles Corridor, said the election is likely to force better thinking about transportation.

"I don't think we should view this as a defeat for transportation but an opportunity to focus on what's practical and realistic, as opposed to what is on our wish list," he said.

Hanley and others said the immediate fallout from the election will reach beyond the Dulles project. Of the $2.75 billion that would have been generated over 20 years from bond sales financed by the tax increase, 40 percent was to go to transit, including VRE rail cars, a trolley on Columbia Pike and maintenance and operation of Metro.

"We're already behind the eight ball," said Pete Sklannik Jr., chief operating officer at VRE, a commuter railroad built to carry 10,000 daily riders but now struggling to accommodate 14,000. "We have an urgent need for seats, an urgent need for parking. It's not going to go away."

Staff writer Lisa Rein contributed to this report.

Virginia Railway Express carries 14,000 riders daily, 4,000 more than planned for. The result is chronic crowding.Virginia Railway Express, whose trains frequently are jammed, had counted on sales-tax revenue to buy 50 new rail cars.