WASHINGTON — The Bush administration urgently pressed Congress in public and private today for quick passage of a $700 billion bailout of the financial industry as Democratic and Republican lawmakers vented their anger over a crisis that slid the nation’s economy toward the brink.

Stocks held steady in pre-noon trading on Wall Street as Treasury Secretary Henry Paulson told the Senate Banking Committee that quick passage of the administration’s plan is “the single most effective thing we can do to help homeowners, the American people and stimulate our economy.”

But even before Mr. Paulson could speak, lawmakers expressed unhappiness, criticism of the plan and — in the case of some conservative Republicans — outright opposition.

“I understand speed is important, but I’m far more interested in whether or not we get this right,” the chairman of the Senate Banking Committee, Senator Dodd, said. “There is no second act to this. There is no alternative idea out there with resources available if this does not work,” he added.

Senator Richard C. Shelby of Alabama, the panel’s senior Republican, was even more blunt. “I have long opposed government bailouts for individuals and corporate America alike,” he said. Seated a few feet away from Mr. Paulson and the chairman of the Federal reserve, Ben Bernanke, he added, “We have been given no credible assurances that this plan will work. We could very well send $700 billion, or a trillion, and not resolve the crisis.”

Mr. Dodd and other key Democrats have been in private negotiations with the administration since the weekend on legislation designed to allow the government to buy bad debts held by banks and other financial institutions.

Key details remain unresolved, although President Bush predicted the Democratic-controlled Congress would soon pass a “a robust plan to deal with serious problems.” He was speaking to the United Nations General assembly.

The Senate hearing unfolded as Vice President Cheney and the Bush administration’s budget director, Jim Nussle, met privately with restive House Republicans. Some members of the GOP rank and file have expressed concerns about the bailout proposal, either because they view it as an unwarranted government intrusion into the financial markets, or because the $700 billion price tag gives them pause.

“Just because God created the world in seven days doesn’t mean we have to pass this bill in seven days,” said Rep. Joe Barton, Republican of Texas.

Added Rep. Darrell Issa, Republican of California, “I am emphatically against it.”

A third witness, the Securities and Exchange Commission chairman, Christopher Cox, urged Congress to regulate a type of corporate debt insurance that figured prominently in the country’s financial crisis.

“I urge you to provide in statute the authority to regulate these products to enhance investor protection and ensure the operation of fair and orderly markets,” he said. The debt insurance is known as credit default swaps.

Despite the bipartisan unhappiness, the prospects for legislation seemed strong, with lawmakers eager to adjourn this week or next for the elections.

Differences remained, though, including a demand from many Democrats and some Republicans to strip executives at failing financial firms of lucrative “golden parachutes” on their way out the door.

The administration is balking at another key Democratic demand: allowing judges to rewrite bankrupt homeowners’ mortgages so they could avoid foreclosure.

The legislation that the administration is promoting would allow the government to buy bad mortgages and other troubled assets held by endangered banks and financial institutions. Getting those debts off their books should bolster their balance sheets, making them more inclined to lend and easing one of the biggest choke points in the credit crisis. If the plan works, it should help lift a major weight off the sputtering economy.

Buttressing Mr. Paulson’s comments, Mr. Bernanke said action by lawmakers “is urgently required to stabilize the situation and avert what otherwise could be very serious consequences for our financial markets and for our economy.”

So far this year, a dozen federally insured banks and thrifts have failed, compared with three last year. The country’s largest thrift, Washington Mutual Inc., is faltering.

Republicans said the sheer size of the bailout would cost each man, woman and child in the United States $2,300.

If approved and implemented, that could push the government’s budget deficit next year into the $1 trillion range — far and away a record.

Senator Obama pointed to other potential consequences, as well. In an interview with NBC, he said that if he wins the White House, he would likely have to phase in the proposals he has outlined for new federal spending. He did not elaborate.

Congressional Republicans, in particular, piled on the criticism of the administration’s suggested solution to the crisis.

“This massive bailout is not a solution, It is financial socialism and it’s un-American,” Senator Jim Bunning, Republican of Kentucky, said.

Mr. Dodd and others indicated that the stakes are too high for Congress not to act, but they made clear they would insist on changes in the administration’s weekend changes.

Mr. Dodd said the administration’s initial proposal would have allowed the Treasury secretary to “act with utter and absolute impunity — without review by any agency or court of law” in deciding how to administer the envisioned bailout program.

“After reading this proposal, I can only conclude that it is not just our economy that is at risk, Mr. Secretary, but our Constitution, as well,” Mr. Dodd said.

America has taken extraordinary measures in recent weeks to prevent a financial calamity, which would have devastating implications for the broader economy. It has, among other things, taken control of mortgage giants Fannie Mae and Freddie Mac, provided an $85 billion emergency loan to insurance colossus American International Group Inc., and temporarily banned short selling of hundreds of financial stocks.