In the future, Richmonders might be able to go to Washington Dulles International Airport by rail and mass transit without driving up Interstate 95.

The federal government reversed itself yesterday and gave preliminary approval to a planned Metrorail expansion in Northern Virginia that would extend the mass transit system through Tysons Corner in Fairfax County and on to Washington Dulles International Airport in Loudoun County.

In a conference call with reporters, Gov. Timothy M. Kaine hailed the Federal Transit Administration's decision, which U.S. Secretary of Administration Mary E. Peters announced yesterday in a letter to Kaine.

The planned 23-mile extension of the subway system is "critical to the success of Dulles," Kaine said, referring to the airport.

"The region is still growing. It must have a robust public transit network," he added.

The FTA had called the project into question in January when it unexpectedly announced that it did not meet federal cost-efficiency standards.

Since then, state officials have been working to meet the federal objections, in part by cutting costs about 10 percent, Kaine said.

Much of the savings was achieved by the state's proposing to fund about $100 million in improvements to state Route 7 from its own transportation fund rather than the Metrorail project, Virginia's deputy Secretary of Transportation Barbara Reese said.

The approval is expected to help the state obtain $900 million in federal funding for the $5 billion plan to extend the system to Dulles.

Kaine said he hoped the approval for the extension would spur Virginia legislators to adopt a new transportation plan that he wants to submit to them in about 10 days.

Kaine noted that a bill adopted by the General Assembly in 2007 that included the now-rejected bad-driver fees dedicated $50 million to Metro funding.

In her letter to the state, Peters noted that extending Metrorail through Tysons Corner will require more maintenance and upkeep of the existing Metrorail system. The Washington Metropolitan Area Transit Authority, an organization that includes Virginia, Maryland and the District of Columbia, has identified $489 million in unfunded capital needs over the next six years, she noted.

"Of all the [federal] concerns [about the project] that are out there, I would say that funding of Metro is the biggest," Kaine said.

Reese said the current timetable, which calls for completing the first phase of the project by the end of 2012 or early 2013, is unchanged.

The first phase would take the Metro through Tysons Corner to Reston. This segment is dependent on federal funding. The second phase, to Dulles, would be funded largely with tolls collected on the Dulles Toll Road.

Legislators from Northern Virginia welcomed the approval.

"Whoever was able to broker the deal, I'll give them a high five," said Del. David B. Albo, R-Fairfax.

State Sen. Patricia S. Ticer, D-Alexandria, a member of the Senate Transportation Committee, said "it is absolutely essential that we have this link."

Contact Tyler Whitley at (804) 649-6780 or twhitley@timesdispatch.com.