WASHINGTON — The House Financial Services Committee pushed forward on Thursday with an aggressive effort to help troubled homeowners, approving legislation that would make up to $300 billion in federally insured loans available to refinance the mortgages of borrowers in danger of foreclosure.

With passage of the House bill virtually assured, debate over how best to address the downturn in housing shifts back to the Senate, where Democrats drafting a similar plan are struggling to overcome the reservations, if not outright opposition, of a more robust Republican minority.

President Bush has called on Congress to pass very specific legislation to update the operations of the Federal Housing Administration, to tighten regulation of the government-sponsored financiers Fannie Mae and Freddie Mac and to let state and local housing authorities use tax-exempt bonds to refinance bad loans. But he opposes the more expansive legislation pursued by Democrats.

The Financial Services Committee approved the bill 46 to 21, with 10 Republicans joining the Democrats in favor of it.

Representative Barney Frank, Democrat of Massachusetts and the chief author of the housing legislation, said Thursday that he hoped President Bush would sign the bill if it reached the White House as part of a wider package and it contained the legislation that Mr. Bush had demanded.

The Democrats’ legislation seeks to help homeowners by requiring lenders to reduce the principal balances for borrowers at risk of default. The bad loans, typically with high adjustable rates, would be refinanced into more affordable 30-year fixed-rate loans insured by the F.H.A.

The new loans would be limited to no more than 90 percent of a property’s value, based on an updated appraisal. The government would retain a stake in any future sale of the property, worth 3 percent of the initial loan balance or 50 percent of net profit from a sale, whichever is greater.

Borrowers would have to demonstrate the ability to repay the new loan, and if they default, they will forfeit the property. Democrats say the plan could help as many as 1.5 million homeowners.

The Bush administration calls that goal unrealistic and says achieving it would require loosening underwriting rules that would put taxpayer money at too much risk. But the administration’s own effort to help troubled borrowers, called F.H.A. Secure, has so far aided only about 2,000 homeowners who were clearly behind in repaying their loans.

In an interview, Mr. Frank said that Republicans, including the president, understood that the government-sponsored lenders were playing an increasingly vital role in the stability of the economy and that they were now anxious to tighten regulation.

“Don’t underestimate the importance” of changes affecting Fannie Mae and Freddie Mac, he said.

As for the Senate, Mr. Frank said: “I am not going to guess.”

Senator Christopher J. Dodd, Democrat of Connecticut and chairman of the banking committee, had been hoping to complete work next Tuesday on a bill that would incorporate the broad expansion of federally insured loans sought by Democrats with a Senate version of the legislation sought by the Bush administration. But aides said a committee vote would be delayed to at least Thursday or perhaps the following week.

In a statement on Thursday, Mr. Dodd said he hoped to reach a deal, even as some Senate Republicans said they remained uncertain.

“Our top priority right now should be helping people keep their homes,” Mr. Dodd said, praising the House committee’s vote. “This is another step in the right direction.”

He added: “I am committed to working on bipartisan legislation with my colleagues in the Senate banking committee to reduce foreclosures and restore liquidity to the mortgage market.”

A spokesman for Senator Richard C. Shelby of Alabama, the senior Republican on the banking committee, declined to comment.

Republican support for the Democrats’ plan has waned in recent days. Senator Mel Martinez, Republican of Florida and a member of the banking committee, who had previously advocated aggressive government action to stem foreclosures, this week said that he supported the more measured response favored by President Bush. Florida is one of the states hit hardest by foreclosures.