WASHINGTON  The Bush administration on Saturday formally proposed a vast bailout of financial institutions in the United States, requesting unfettered authority for the Treasury Department to buy up to $700 billion in distressed mortgage-related assets from the private firms.

The proposal, not quite three pages long, was stunning for its stark simplicity. It would raise the national debt ceiling to $11.3 trillion. And it would place no restrictions on the administration other than requiring semiannual reports to Congress, granting the Treasury secretary unprecedented power to buy and resell mortgage debt.

“This is a big package, because it was a big problem,” President Bush said Saturday at a White House news conference, after meeting with President Álvaro Uribe of Colombia. “I will tell our citizens and continue to remind them that the risk of doing nothing far outweighs the risk of the package, and that, over time, we’re going to get a lot of the money back.”

After a week of stomach-flipping turmoil in the financial system, and with officials still on edge about how global markets will respond, the delivery of the administration’s plan set the stage for a four-day brawl in Congress. Democratic leaders have pledged to approve a bill but say it must also include tangible help for ordinary Americans in the form of an economic stimulus package.