FAIRFAX, Va. — Barack Obama yesterday launched his campaign to sell what may be the most ambitious government spending plan in American history, urging Congress to act swiftly on his upcoming proposal to jump-start the economy or risk dooming the country to a diminished future.

"We should have an open and honest discussion about this recovery plan in the days ahead," Obama said in a half-hour televised speech given before an invitation-only audience at George Mason University in suburban Washington.

"But I urge Congress to move as quickly as possible on behalf of the American people. For every day we wait or point fingers or drag our feet, more Americans will lose their jobs. More families will lose their savings. More dreams will be deferred and denied. And our nation will sink deeper into a crisis that, at some point, we may not be able to reverse."

His stark message was an extraordinary move, coming from a man who hasn't yet taken office as president and has yet to offer any details of his plan. However, he also noted that these are extraordinary times.

"I don't believe it's too late to change course, but it will be if we don't take dramatic action as soon as possible," he said.

"If nothing is done, this recession could linger for years. The unemployment rate could reach double digits," Obama continued. "Our economy could fall $1 trillion short of its full capacity, which translates into more than $12,000 in lost income for a family of four. We could lose a generation of potential and promise, as more young Americans are forced to forgo dreams of college or the chance to train for the jobs of the future. And our nation could lose the competitive edge that has served as a foundation for our strength and standing in the world."

Obama acknowledged that his effort has grown more difficult with the forecast that this year's federal budget deficit will reach a record $1.2 trillion.

"I understand that some might be skeptical of this plan. Our government has already spent a good deal of money, but we haven't yet seen that translate into more jobs or higher incomes or renewed confidence in our economy," he said.

"There is no doubt that the cost of this plan will be considerable. It will certainly add to the budget deficit in the short term. But equally certain are the consequences of doing too little or nothing at all, for that will lead to an even greater deficit of jobs, incomes and confidence in our economy."

As negotiations with Congress accelerated behind closed doors, Obama urged around-the-clock work to get a proposal ready and through Congress soon after he takes office Jan. 20.

Key members of Congress warned that the next few weeks could be rocky as various factions wrestle over the details, but they expressed unusual confidence that they could write and pass the huge plan in time for Obama to sign it into law by Presidents Day on Feb. 16.

House Speaker Nancy Pelosi, D-Calif., said she'll keep the House of Representatives in session through a scheduled 10-day Presidents Day recess if necessary to pass the plan.

Republicans lauded Obama for reaching out to them, but withheld support until they see the details.