He argued, nonetheless, that it is time "to act boldly" and not be intimidated by the cost, because "the consequences of doing too little or nothing at all ... will lead to an even greater deficit of jobs, incomes, and confidence in our economy."
Obama's appeal for public support of his spending plan is coupled with a vow to bolster and reform Wall Street.
While promising to protect companies "whose collapse could endanger the entire economy," Obama said, "no longer can we allow Wall Street wrongdoers to slip through regulatory cracks. No longer can we allow special interests to put their thumbs on the economic scales."
ABC News has confirmed that Obama will name Harvard University law professor Cass Sunstein to be his regulatory czar. The appointment of Sunstein, who was friends with Obama while they were both faculty members at the University of Chicago Law School, indicates a more activist approach to regulation than was taken by the Bush administration.
If all goes according to plan, the economy can start showing some growth at the end of this year, he says.
Not everyone is confident that Obama's plan will work or work on his timetable.
"For something like this to really take hold, it could take several years," Andrew Ross Sorkin of the New York Times tells "Good Morning America" today.
Liz Ann Sonders, chief investment strategist for Charles Schwab & Co., tells "GMA" that "time as much as anything else" is the cure the economy.
"There's this confidence crisis that still hasn't been quite cracked, and I think we're starting to see that come undone a bit," Sonders says.
Sorkin says it is important for Obama to "manage expectations."
"The political backlash if we do not see results and we don't see them quickly is going to be tough," Sorkin warns.
Dave Ramsey, of the "Dave Ramsey Radio Show," questioned the necessity of Obama's massive spending plan.
"What really drives the economy? Is it D.C.'s programs, or is it business people out here in the fruited plains?" Ramsey asks.
"This thing will begin to heal itself. Do we have to go $1 trillion in debt to that?" he asks.
Ramsey added that it's most important for Obama to instill confidence in the country's economic system.
"Whether you agree with the spending or not, my hope is that this president-elect will instill some confidence in people, not necessarily what he's doing is going to fix everybody everything. But just generally everything is going to be OK."
ABC News' Jonathan Karl contributed to this report