The head of the Federal Transit Administration on Tuesday said there is no certainty the federal government will provide the hundreds of millions of dollars in federal funding anticipated for the Dulles Corridor Metrorail Project — even if the new tracks run above Tysons Corner.

FTA Administrator James Simpson, at a press conference rolling out the Bush administration’s $1.4 billion “New Starts” spending plan for major transit projects, asserted the $900 million federal share for the rail extension is not yet committed, despite contrasting media and state official reports. The possible loss of the money is at the center of the debate over whether the rail should run above or below Tysons Corner.