Christina Romer, whom Mr. Obama has designated to be his chief economist, concluded in research she helped write in 1994 that interest-rate policy is the most powerful force in economic recoveries and that fiscal stimulus generally acts too slowly to be of much help in pulling the economy out of recessions, though associates said she now supports a big stimulus package if policy makers roll it out early enough in the recession.

The goal behind all those ideas is to jump-start economic activity by getting as much money as possible as quickly as possible into the hands of consumers and businesses, trying to make up for the falling demand in the private sector that is leading to higher unemployment. And although the package includes a big dose of tax cuts, it represents a big departure from President Bush’s playbook by relying heavily on direct government spending.

“This is not an intellectual exercise, and there’s no pride of authorship,” Mr. Obama told a news conference in Washington on Friday. “If members of Congress have good ideas, if they can identify a project for me that will create jobs in an efficient way  that does not hamper our ability to, over the long term, get control of our deficit; that is good for the economy  then I’m going to accept it.”

Mr. Obama’s aides said he did not intend to unveil a detailed formal proposal but rather to allow Congress to fill in the outline that he has proposed.

Given the recent scale of the downturn  the nation lost 1.5 million jobs in the last three months of 2008, and economic output during those months shrank by 6 percent compared with same period in 2007  economists were highly uncertain about whether the economic plan would provide enough firepower.

Adam Posen, the deputy director of the Peterson Institute for International Economics in Washington, said Mr. Obama’s plan could provide just the right boost  if it was carried out properly.

But as the Federal Reserve has been learning for months now, the biggest obstacle to economic activity right now is not a shortage of money. The real obstacle is pervasive fear, which has made banks reluctant to lend and companies reluctant to invest in expansion.