President Barack Obama said Wednesday the recession will turn into "a catastrophe" if the economic stimulus is not passed quickly, lobbying anew for the plan as its price tag climbed above $900 billion and drew more criticism.

The president rejected several complaints about the plan, including arguments that tax cuts alone would solve the problem or that longer-term goals such as energy independence and health care reform should wait. Obama opposed such piecemeal approaches.

Instead, he argued that recalcitrant lawmakers need to get behind him, saying the American people embraced his ideas when they elected him president in November.

While urging members of Congress to act swiftly, he also promised to make changes to the legislation, which has been criticized as larded with spending that won't have an immediate impact on the economy.

"No plan is perfect, and we should work to make it stronger," Obama told reporters at the White House. "Let's not make the perfect the enemy of the essential. Let's show people all over our country who are looking for leadership in this difficult time that we are equal to the task."

Obama has sought each day to ratchet up the pressure on lawmakers, bringing different supportive groups to the White House, scheduling a series of TV interviews, even traveling to a charter school to tout one portion of the bill.

"A failure to act, and act now, will turn crisis into a catastrophe and guarantee a longer recession, a less robust recovery, and a more uncertain future," he said. "That's why I feel such a sense of urgency about the Economic Recovery and Reinvestment Plan."

The Senate added money to its version of the bill for medical research and tax breaks for car purchases. The price tag could go yet higher Wednesday if a tax break for homebuyers is made more generous, even as centrists in both parties promise to clear away spending items that won't jump-start the economy immediately.

In an interview on CNN on Tuesday, Obama signaled a willingness to drop items that "may not really stimulate the economy right now." He also signaled he'll try to remove "buy American" provisions in the legislation to avoid a possible trade war.

In a victory for auto manufacturers and dealers, Sen. Barbara Mikulski, D-Md., won a 71-26 vote to allow most car buyers to claim an income tax deduction for sales taxes paid on new autos and interest payments on car loans. The break would cost $11 billion over the coming decade but could mean savings of $1,500 on a $25,000 car.

"Just as we need to get the housing market going, we need to get auto sales going," said Sen. Debbie Stabenow, D-Mich.

Wednesday's session could produce even more generous savings for homebuyers.

Sen. Johnny Isakson, R-Ga., is pressing for a tax credit of up to $15,000 for everyone who buys a home this year, at a cost of $18.5 billion. The pending measure would award a $7,500 tax credit only to first-time homebuyers.

At the same time, centrist senators, including Ben Nelson, D-Neb., and Susan Collins, R-Maine, are seeking to cut tens of billions of dollars from the legislation. They're operating with the blessing of Democratic leaders, who hope a successful effort could attract some GOP votes for Obama's plan.

Obama summoned Collins to a White House meeting Wednesday afternoon, a Collins aide said.

Democratic leaders conceded they may soon be obliged to cut billions of dollars from the measure. "It goes without saying if it's going to pass in the Senate, it has to be bipartisan," said Sen. Dick Durbin of Illinois, the second-ranking Democratic leader, adding that rank-and-file lawmakers in both parties want to reduce the cost of the bill.

In a series of skirmishes Tuesday, the Senate turned back a proposal to add $25 billion for public works projects and voted to remove a $246 million tax break for movie producers. Both moves were engineered by Republicans who are critical of the bill's size and voice skepticism of its ability to create jobs.

But several hours later, GOP conservatives didn't contest approval of a $6.5 billion increase in research funding for the politically popular National Institutes of Health. That amendment, by Tom Harkin, D-Iowa, drove the price tag of Obama's plan just above $900 billion.

Democratic leaders have pledged to have the bill ready for Obama's signature by mid-month.