WASHINGTON (AP) — Top Democrats plan to add a big increase in highway and mass transit funding to President Barack Obama's economic recovery program Tuesday, even as others in the president's party hope to rein in the plan's almost $1 trillion cost to taxpayers.

A move by Patty Murray, D-Wash., to add $25 billion in infrastructure projects is first in line as the Senate begins thrashing through dozens of proposed changes to the sprawling $885 billion measure.

Murray's plan would increase the money in the bill for highway projects by almost 50 percent, to $40 billion, reflecting complaints from lawmakers in both parties that Obama's plan doesn't do enough to relieve a backlog of unfinished projects. Mass transit programs would get a $5 billion boost, while water projects would get $7 billion more.

Republicans, for their part, readied a plan to lower mortgage costs to try to jolt the housing market out of its slump.

The $885 billion Senate economic plan faces assaults from both Democrats and Republicans during debate this week, as lawmakers in both parties aim to kill ideas that won't jolt the economy right away.

"The goal is to shape a package that is more targeted, that would be smaller in size and that would be truly focused on saving or creating jobs and turning the economy around," said Sen. Susan Collins, R-Maine. She said ideas like $870 million to combat bird flu should be dumped.

Democrats already are under pressure from moderates in their own party to scale back spending in the $885 billion bill, and Obama met with party leaders at the White House late Monday to discuss strategy.

"What we can't do is let very modest differences get in the way" of swift enactment of the legislation, Obama said several hours earlier as new layoffs rippled through the economy and the Commerce Department reported an unexpectedly large sixth straight drop in personal spending.

In the Capitol, Republicans said their goal was to change the bill, not to block it. "Nobody that I know of is trying to keep a package from passing," said Sen. Mitch McConnell of Kentucky, the Republican leader.

"We need to fix housing first," he said. Republicans are expected to seek a vote on their proposals this week as part of the debate on the overall stimulus measure.

Officials said the GOP was coalescing behind a proposal designed to give banks an incentive to make loans at rates currently estimated at 4 percent to 4.5 percent. Fannie Mae and Freddie Mac, which were seized by the federal government in September, would be required to purchase the mortgages once banks have made them to consumers.

Officials said loans to credit-worthy borrowers on primary residences with a mortgage of up to $625,000 would qualify, including those seeking to refinance their current loans.

Separately, Republican officials said they intended to press for a $15,000 tax credit for home buyers through the end of the year. Current law permits a $7,500 tax break and limits it to first-time home buyers.

Nineteen Democratic and Republican governors, meanwhile, cited frozen credit markets and rising unemployment in urging lawmakers to resolve their differences and asking Obama to sign the bill as soon as it reaches his desk. The governors said the money it provides for public education, health care and rebuilding the nation's infrastructure will create and preserve jobs while making a sound investment in the country's long-term economic interests.

"While we all believe in the importance of free markets, we believe that the markets today need stimulating," the governors told Obama in a letter dated Monday. Among the signers are Democrats Deval Patrick of Massachusetts and Tim Kaine of Virginia, and Republicans Arnold Schwarzenegger of California and Charlie Crist of Florida.