A foreclosure aid plan that was facing a sluggish trip through Congress has a powerful new engine behind it: the Bush administration's urgent request to rescue mortgage giants Fannie Mae and Freddie Mac.

Lawmakers have little choice but to give the government power to send a lifeboat to the two companies to prevent an election-year economy from drowning in mortgage defaults. The quicker they do it, the sooner 400,000 strapped homeowners could get new, cheaper loans instead of losing their homes.

"The silver lining on this cloud is that it dissipates any question about how this bill is going to get passed," Rep. Barney Frank, D-Mass., the Financial Services Committee chairman, said of a broader housing package.

The House approved its version in May and the Senate followed suit on Friday, but a veto threat from President Bush and lawmakers' disputes over key details were threatening to sap its momentum.

Now it's clear the package — which also includes modernizing the Federal Housing Administration and creating a new regulator and tighter controls for Fannie Mae and Freddie Mac — has to move quickly. Frank said the House would act by Friday to resolve lingering differences and add authority for the government to prop up the mortgage giants if needed, in hopes that the Senate would agree and clear the measure for Bush next week.

"I'm confident we're going to get this done," said Sen. Christopher J. Dodd, D-Conn., the Banking Committee chairman. "Unfortunately, these events over the last few days have probably increased the importance of this in the minds of some."

The administration, which has criticized key elements of the broad housing package, now has a powerful incentive to work out differences with Democratic leaders, who relish the prospect of claiming credit for a homeowner rescue plan just months before voters go to the polls.

And holdout Republicans, including Minority Leader John A. Boehner of Ohio and Whip Roy Blunt of Missouri, will find it more difficult to bash a plan that includes measures their own president calls crucial.

Shortly after Treasury Secretary Henry M. Paulson announced his plan to offer help to Fannie and Freddie, the two issued a statement saying they "stand ready" to work with him and congressional Democrats "to take appropriate steps to ensure the soundness of our mortgage markets."

"I think people understand the urgency of needing to get this (housing) bill done. And it's fortunate that we have this vehicle to be able to tack this on," said Dana Perino, a White House spokeswoman.

Still, GOP conservatives concerned about the government sending aid to the private companies will likely try to slow the legislation. In a letter to Frank and House Speaker Nancy Pelosi, D-Calif., Rep. Jeb Hensarling, R-Texas, called for hearings.

"We appreciate that our housing finance and capital markets are at a critical juncture due to scarce liquidity and waning investor confidence. However, given that a decision of this magnitude will affect the lives of each and every American for years, even decades, to come, it is essential that Congress fully consider these proposals and all the alternatives," Hensarling wrote in a letter circulated Monday.

Republicans have consistently bristled against the idea of allowing what they call a government bailout of irresponsible homeowners who borrowed more than they could afford and unscrupulous lenders who preyed on unwitting or reckless buyers.

That's how many of them describe the mortgage rescue plan, which allows the FHA to back an additional $300 billion in new mortgages so homeowners who can't afford their payments and would normally be considered too financially risky to qualify could refinance into more affordable, fixed-rate loans. The program would guarantee some payoff for lenders who took substantial losses on the distressed loans, in many cases letting them recover more than they could in a costly foreclosure.

Critics have struggled to explain their opposition to the plan in light of the government's actions earlier this year to rescue failing investment bank Bear Stearns. Now, with the Federal Reserve and Treasury making it clear they would swoop in to offer similar help to Fannie and Freddie, the homeowner aid program appears to have gained more legitimacy.

Frank argued Congress isn't just handing out credit; it's also moving to prevent a future market meltdown like the one officials are hoping to head off with the newly announced plan.

"We are not simply making the credit available, we are simultaneously making sure it won't happen again," through stricter regulations on Fannie and Freddie and allowing more homeowners to borrow safely through the FHA rather than with shady subprime mortgages.

Proponents of the housing package said the problems for the mortgage giants — whose stocks plummeted on investor fears about their financial health in light of their outsized role in the home loan market — shouldn't interfere with their ability to pay for any losses from the homeowner rescue, as required by the bill.

"There has been fear," Dodd said. "But fear is not a fact, and the fact is Fannie and Freddie are in sound shape."

Lawmakers still must cut deals on key details, chief among them the limits governing the loans the companies may buy and the FHA may insure. The House places the cap around $730,000 while the Senate's is at $625,000.

The House will likely drop $3.9 billion from the Senate-passed bill for buying and rehabilitating foreclosed properties — the White House's biggest gripe with the bill — which Democrats hope to tack on instead to a must-pass spending bill.