Congressional Republicans reacted skeptically, just as Mr. Obama acknowledged he would be forced to recant some of his campaign promises given the economic situation. Even his own economists acknowledged their two-year estimates could be wrong.
The 14-page analysis says estimates are "subject to significant margins of error" -- because of the assumptions that went into the economic models and because it is not known what might pass Congress.
"These numbers are a stark reminder that we simply cannot continue on our current path," Mr. Obama said in his weekly radio and YouTube broadcast address.
The president-elect has provided few details of his $775 billion plan. This fresh report does not include the specific construction of his tax cuts or the amounts dedicated to state aid and public works.
On Saturday, economic aides and advisers declined to lay out even rough estimates for the plan's components. They said they worked with broad instructions from Mr. Obama but didn't want to limit negotiations with congressional leaders by outlining their limits in public.
"I want to be realistic here. Not everything that we talked about during the campaign are we going to be able to do on the pace we had hoped," Mr. Obama told ABC's This Week for an interview set to air today.
For a second time since his election, Mr. Obama increased the number of jobs his program would create, taking the number to as many as 4.1 million saved or created -- a benchmark his critics charge cannot be measured. During the campaign, he promised only 1 million new jobs.
The analysis came out one day after news the unemployment rate had jumped to 7.2 percent, the highest in 16 years.
GOP lawmakers have insisted on carefully targeting any aid and on a politically popular tax cut for the middle class, in addition to loans to states.
"We want to make sure it's not just a trillion-dollar spending bill, but something that actually can reach the goal that he has suggested," said Sen. Mitch McConnell of Kentucky, the Senate's top Republican.
The new report is likely to intensify debate as economists outside the Obama team begin delving into the analysis. The report, for example, estimates the unemployment rate at the end of 2010 would be 1.8 percentage points lower if the plan is enacted.