McLEAN -- The federal government has given tentative approval to a planned Metrorail extension in northern Virginia.

The approval announced today is a critical step toward obtaining the needed $900 million in federal funding for the $5 billion project. It would extend the transit system through Tysons Corner and on to Dulles International Airport in Loudoun County.

The project's future had been in doubt since January, when the Federal Transit Administration unexpectedly announced that the project did not meet federal cost-efficiency standards. Virginia has been scrambling for months to bring the project into compliance.

Federal Transit Administrator James Simpson says the proposal has improved since January. He says his agency will commit $159 million toward completing final design and engineering, but says more work is needed before the feds will commit any construction funds.

-- The Associated Press