He called the plan "big enough to meet the challenges we face" and said that it will jump-start job creation but also "lay the foundation for a strong and growing economy."
Aides said the economic plan outlined Saturday went further that the president-elect has gone before.
A trio of crises - housing, credit and financial - have badly damaged the economy, and financial analysts have projected the country's economic hardships will continue through much of 2009.
Obama acknowledged Saturday that evidence is growing the country is "facing an economic crisis of historic proportions." He noted turmoil on Wall Street, a decrease in new home purchases, growing jobless claims and the menacing problem of deflation.
He said he was pleased Congress passed an extension of unemployment benefits this week, but added, "We must do more to put people back to work and get our economy moving again."
Figures out this week showed new claims for jobless aid had reached a 16-year high. "If we don't act swiftly and boldly, most experts now believe that we could lose millions of jobs next year," Obama said.
He cautioned, "There are no quick or easy fixes to this crisis, which has been many years in the making, and it's likely to get worse before it gets better." But Obama said Inauguration Day, Jan. 20, "is our chance to begin anew."
Obama said getting congressional approval for his broad economic plan will not be easy.
"I will need and seek support from Republicans and Democrats, and I'll be welcome to ideas and suggestions from both sides of the aisle," he said. "But what is not negotiable is the need for immediate action."
Across the country, Americans "are lying awake at night wondering if next week's paycheck will cover next month's bills," people are showing up at work to clear out their desks and retirees are watching their life savings disappear, Obama said.
