WASHINGTON — Seeking to gird the nation's economy against a potential tidal wave of foreclosures, the Bush administration will release a plan today that is expected to block many mortgages from adjusting to higher rates for up to five years.

Administration officials conceded privately yesterday that the plan is likely to face objections from low-income borrowers who won't be helped and from investors who backed now-troubled subprime loans at the heart of the mortgage crisis.

But they said the goal is to keep rising foreclosures from tilting the broader economy toward recession, and that helping specific groups was a secondary objective.

"Foreclosure prevention is the goal," said one official, who spoke on condition of anonymity because the plan had not yet been announced. "There are going to be questions, for sure, no matter how it's done."

Treasury Secretary Henry Paulson, in a speech Monday, called the housing market downturn "the biggest challenge to our economy."

"When home foreclosures spike, the damage is not limited only to those who lose their homes," Paulson said. "Homes in foreclosure can pose costs for whole neighborhoods, as crime goes up and property values decline. Avoiding preventable foreclosures, then, is in the interest of all homeowners."

In addition to freezing some mortgages that otherwise would carry much higher interest rates and monthly payments, the plan calls for speeding up the process of bringing lenders and low-income homeowners together to renegotiate mortgages on terms that the borrowers can afford.

Such deals mean lenders receive less than the sharply higher rates called for in the original adjustable-rate loans but more than many would receive through foreclosure.

Just which borrowers receive help could become a sticking point, however.

As talk of a rate freeze gathered traction in recent weeks, some critics complained that lenders would be bailing out people who knowingly took out bigger loans than they could afford in hopes of reaping windfall profits as home values soared.

Some members of Congress have made clear to the administration that the plan needs to exclude real-estate speculators.

"We strongly support steps by lenders to help those Americans facing foreclosure to restructure their loans and keep their homes," four House members — two Democrats and two Republicans — wrote in a letter to John G. Stumpf, chief executive of Wells Fargo.

"However," they were quick to add, "it should be noted that our call for assistance does not include those involved in fraudulent behavior, illegal immigrants or so-called 'flippers,' who own investment properties that are not primary residences."

The letter was signed by Reps. Paul E. Kanjorski, D-Pa., Judy Biggert, R-Ill., Carolyn B. Maloney, D-N.Y., and Deborah Pryce, R-Ohio, all of whom hold senior positions on the House Financial Services Committee.

On the other side, consumer advocates contend that many borrowers were victims of overzealous mortgage loan brokers, who pushed people into taking out new loans or refinancing to earn rich commissions. Last year, the parent company of Ameriquest Mortgage Co. agreed to pay $325 million to settle claims by state regulators that it had engaged in an array of predatory lending practices.

Mortgage loan data also show that many people who could have qualified for low-cost prime loans instead took out higher-cost subprime loans designed for people with shaky credit. Critics say that is a sign of unscrupulous brokers, who earn bigger commissions on subprime loans.

"The industry should not continue to be unjustly enriched by profits they derived by putting people into higher-interest, adjustable subprime loans when the same borrowers had actually qualified for lower-interest, fixed-rate loans," California Democratic Assemblyman Ted Lieu said.

Lieu called on President Bush to expand his proposal to freeze rates for all subprime borrowers who could have qualified for prime loans. "Unfortunately, for many of them, the Bush plan will do nothing to help."

Administration officials say they understand such complaints but that their first priority is protecting the larger economy, which could be dragged into recession if the crisis in the housing sector intensifies.

As many as 2 million adjustable-rate subprime mortgages will reset to higher interest rates and payment levels in the next year. If borrowers can't make those higher payments, the properties could slip into foreclosure and further weaken home values, and the economy with it.

The five-year freeze will be offered to borrowers who live in their homes, are current on their mortgage payments, have accrued at least some equity in their homes and whose income indicates they cannot afford higher payments.