NEW YORK (CNNMoney.com) -- President Bush asked Congress on Saturday for the authority to spend as much as $700 billion to purchase troubled mortgage assets and contain the financial crisis.

The legislative proposal - the centerpiece of what would be the most sweeping economic intervention by the government since the Great Depression - was sent by the White House overnight to lawmakers. (Read the text here.)

The plan matches the scope of the problem, Bush said.

"It is a big package because it's a big problem," Bush told reporters at a news conference. "The risk of doing nothing far outweighs the risk of the package."

Treasury Secretary Henry Paulson, lawmakers and their aides are expected to work through the weekend in an effort to craft a bill swiftly. Democratic leaders on Capitol Hill said they expect the bill to go before a vote within days.

Paulson, Federal Reserve Chairman Ben Bernanke and other officials have said in recent days that the lack of easy credit between banks and other financial institutions threatens to inflict serious damage on the economy if not addressed immediately.

"This program is intended to fundamentally and comprehensively address the root cause of our financial system's stresses," according to a Treasury statement released Saturday. "As illiquid mortgage assets block the system, the clogging of our financial markets has the potential to significantly damage our financial system and our economy, undermining job creation and income growth."

The plan would allow the Treasury to buy up mortgage-related assets.

The aim is for the government to buy the securities at a discount, hold onto them and then sell them for a profit.

This proposal has been compared to the Resolution Trust Corp., which was put in place during the savings and loan crisis to administer and sell assets from failed thrifts.

However, experts say the Treasury's plan is more akin to the Home Owners' Loan Corp., put in place in 1933 to stem foreclosures and help refinance defaulting mortgages and boost banks' liquidity.

The mortgage plan is part of an extraordinary effort by the federal government to contain a financial crisis that has forced a major realignment on Wall Street and has started rippling out to Main Street.

In the past week, two of the nation's most venerable investment banks - Lehman Brothers (LEH, Fortune 500) and Merrill Lynch (MER, Fortune 500) - have fallen and the Federal Reserve was forced to lend $85 billion to prevent the sudden collapse of insurance giant American International Group (AIG, Fortune 500).

Meanwhile, mainstay financial institutions are scrambling to raise cash and shore up their books as lending has frozen up and investor confidence has sunk.

Raising the debt ceiling, judging the cost

The administration's proposal also requests that Congress authorize an increase to the nation's debt ceiling. Currently, it's set to rise to $10.6 trillion for fiscal year 2009 - which runs from October 2008 through September 2009. But the proposal requests that limit be increased to $11.315 trillion to allow for the purchases of mortgage-backed assets.

The debt limit is a ceiling on how much debt the federal government is allowed to take on. Budget experts say it acts as a break on spending mostly because of political pressure, because lawmakers don't like to vote to raise it. Lawmakers are free to change it if they have reason, however.

The cost of the bailout to taxpayers may hinge on the price at which the Treasury buys the mortgage securities.

"The government could make a profit, a substantial profit," said Jaret Seiberg, a financial services analyst at the Stanford Group, a policy research firm. "The pricing mechanism is going to be central."

The jury is still out on whether the proposal will fix the financial crisis, although experts are cautiously optimistic the plan will help the housing crisis. It will help banks shore up their balance sheets by removing hard-to-value assets. This would address the seemingly endless rounds of writedowns and capital raising that have been rocking the financial sector.

Without these bad loans weighing on their books, banks may be more willing to lend. Or at least that's the goal.

The problem is that the bailout will not automatically make banks profitable, nor can it immediately stop the slide in home values that is wreaking havoc on the economy.

Reaction on the Hill

Key lawmakers and their staffers will be in talks about the proposal with Treasury staff over the weekend. Although they've said they don't want the negotiations to turn the bill into a "Christmas tree" of provisions, Democrats are concerned that there be measures included to protect taxpayers and help homeowners directly.

Paulson said Sunday that the government's first priority needs to be focused on getting Congress to pass the massive package. "The credit markets are still very fragile right now and frozen," Paulson said in an interview on NBC's Meet the Press, according to the Associated Press. "We need to deal with this and deal with it quickly."

Paulson was making the rounds on the television talk shows Sunday morning.

He also said that "it pains me tremendously to have the American taxpayer put in this position but it is better than the alternative," according to the AP.

In a statement Saturday, Sen. Charles Schumer, D-N.Y., co-chairman of the Joint Economic Committee, called the proposal "a good foundation ... that can stabilize markets quickly."

"But it includes no visible protection for taxpayers or homeowners," Schumer said. "We look forward to talking to Treasury to see what, if anything, they have in mind in these two areas."

House Minority Leader John Boehner, R-Ohio, said the economy is facing "unprecedented financial challenges that could imperil the bank accounts, retirement savings, and jobs of countless Americans." He called on fellow lawmakers to "work together to solve this crisis."

Treasury officials briefed congressional staffers Saturday on the details of the plan. An hour-long closed-door meeting was attended by about 25 top aides to the congressional leadership from both parties as well as the key committee aides who will oversee the new program. At least one White House legislative affairs staffer was also in the meeting.

One Democratic aide, who also declined to be named, said the plan is "complicated" and the Treasury officials were "very forthcoming" about how the plan will work.

"No one likes it," the aide said. "But everyone knows we need it."

In the House, Conservative Republican lawmakers who groused earlier this week about "bailout mania" gripping Washington held a conference call to discuss the plan.

"We believe it is as dire as Paulson says it is," one of the lawmakers, who asked not to be identified, told CNN. "We think it is a fait accompli and don't have the wherewithal to stop it."

While it may not be stopped, some expect it still may be amended.

"Stability benefits everyone, but there is little in the bill that lawmakers can point to and say that this will aid their constituents," said Seiberg, the banking expert. "That is why we expect other provisions to get added by Congress, such as a clause that clearly states that Treasury has an obligation to try to restructure troubled mortgages that it acquires."

Indeed, after a conference call Saturday afternoon with other House Democratic leaders, House Speaker Nancy Pelosi, D-Calif., said in a statement that Democrats would seek to "insulate Main Street from Wall Street and keep people in their homes by reducing mortgage foreclosures."

"(We) will strengthen the proposal by ensuring that the government is accountable to the taxpayers in any future actions under this broad grant of authority, implementing strong oversight mechanisms, and establishing fast-track authority for the Congress to act on responsible regulatory reform," Pelosi said.

CNN congressional producers Deirdre Walsh and Ted Barrett, correspondent Kate Bolduan and CNNMoney.com senior writer Tami Luhby contributed to this report.