President Bush wants to convert $2 billion in unused 9/11 tax credits to help build the long-proposed rail link between Lower Manhattan and JFK Airport.

Yesterday’s announcement was not a complete surprise: Bush had put the measure in last year’s budget, but it was killed by the Republican Congress. Its chances may be better this time with Democrats in control. Two of the link’s biggest boosters are Sen. Charles Schumer and Rep. Charles Rangel.

Slammed as a waste of money by transit advocates, the $7 billion rail link has never lost support from politicians and the downtown business community, which has lobbied hard for the express train service that would also connect Long Island and Queens to the tip of Manhattan. Schumer released a statement yesterday citing the need of downtown businesses to draw from “the labor pool in Long Island.”

Mayor Michael Bloomberg applauded the proposal, saying it would “spur job growth” and “ease crowding on subways.”

“This isn’t final,” said Gene Russianoff of the Straphangers Campaign, a critic of the project. “It’s a proposal in a budget that’s going to get sliced and diced. When all the tough choices are made, Congress may not find the $2 billion.”