WASHINGTON — As Congress and the Bush administration scramble to reach an accord on a plan to jump-start the ailing economy, Mayor Bloomberg is deriding the consensus proposal for a stimulus package as a shortsighted “quick fix” that would have little long-term benefit.

Mr. Bloomberg arrived here last night to accept the President’s Award from the U.S. Conference of Mayors, and he promptly threw cold water on the rare burst of bipartisanship that has brought together Democratic leaders and the White House to hammer out an economic stimulus plan.

The $145 billion proposal being negotiated centers around the idea of providing several hundred dollars in tax rebates to individuals and families in a bid to spur the economy — a plan that Mr. Bloomberg said could “modestly benefit Americans” but would not “make a huge difference” overall because of the enormous deficits the government has already run up.

“We can’t borrow our way out of this problem. The jig is up,” the mayor said in a 20-minute speech at the National Building Museum. “It’s time to start getting our house in order once and for all, which I believe starts with a simple idea: making decisions based on the business cycle instead of the election calendar.”

Mr. Bloomberg spoke hours after the Dow Jones Industrial Average rallied for a nearly 300-point gain, ending a volatile day that saw stocks plummet more than 250 points in the early hours of trading.

Invoking an oft-repeated quote from President Kennedy, Mr. Bloomberg contrasted what he described as “reckless” spending in Washington with his own record in New York, characterizing as prescient his decision to use surplus funds accrued in recent years to pay down future deficits and establish a trust fund for municipal retirees.

“John F. Kennedy told us, ‘The time to repair the roof is when the sun is shining.’ That’s what many of us in this room actually did,” Mr. Bloomberg said.

“But if you take a look at the federal government here in Washington,” he added, “they did exactly the opposite. They spent most of this decade when things were good running up bills with reckless abandon and when the economy started heading for the ditch, the special interest giveaways got even bigger.”

The mayor then offered a farming analogy to the crowd of urban leaders. “They ate the seed corn without worrying about the next year’s crop,” he said. “Well, here we are, the seed corn is gone. All we’ve got is an armful of IOU’s.”

Mr. Bloomberg called for a combination of short-term and long-term measures to respond to the subprime mortgage crisis and shore up the economy. He stopped short of backing a full government bailout for either borrowers or the mortgage industry, but he also criticized the centrality of tax rebates in the current plan. “What good is a rebate going to do a family who’s about to lose the place where they sleep in?” he said. He suggested financial counseling and subsidized loans for people trapped in bad mortgages.

Mr. Bloomberg endorsed New Deal-style federal investment in infrastructure projects that states and cities couldn’t afford, saying it would create jobs and build a foundation for the future. Congressional Democrats have also proposed infrastructure spending as a way to boost the economy.

The mayor has crisscrossed the country waging what some observers view as a shadow campaign for the presidency. He has decried partisanship and gridlock in Washington, but the bipartisan effort on the stimulus package has failed to quiet his criticism. “The problems of our economy are not going to be solved with a quick fix,” he said. “We need policies that will produce a boost in the short term, and most importantly, a boom in the long term.”

Mr. Bloomberg spoke as congressional leaders and Bush administration officials were attempting to finalize an agreement on a stimulus package, which would include an extension of unemployment benefits and an increase in food stamp benefits in addition to the rebates for taxpayers promised by the president.

Led by the chairman of the House Ways and Means Committee, Rep. Charles Rangel of Harlem, Democrats were also pushing for more aid targeted to low-earning Americans who do not pay income taxes.

While party leaders, including Senator Schumer, have said Democrats would not draw a “line in the sand” on the issue, Mr. Rangel rushed out a statement yesterday afternoon reiterating his commitment to aid for non-taxpayers as a response to reports that Republican leaders were balking.

A member of the Democratic leadership who serves on the Ways and Means Committee, Rep. Joseph Crowley of New York, said the goal of a stimulus package was to get money in the hands of the people who were most likely to spend it immediately, and, largely for reasons of necessity, that demographic is low-income Americans.

Leaders in Washington are under intense pressure to reach an agreement quickly, as economists warn that a stimulus package needs to be implemented soon to have any chance of averting a recession that some say may already be under way. It would likely take at least six weeks for the government to begin sending rebates even after both houses of Congress and the president approved legislation.

“When you need stimulus you cut checks. You’ve got to get the money out the door,” a senior economic adviser to Senator Obama, Austan Goolsbee, said yesterday at a campaign panel organized by the New America Foundation.

With public approval for Congress and President Bush near an all-time low, and with Wall Street looking to Washington for signs of economic stability, the risk of delay or inaction is high.

“There’s a credibility issue on the line for both the White House and the Congress,” Mr. Crowley said in an interview. “It’s a pox on both our houses if we don’t get something done.”

Republican leaders were facing mounting pressure yesterday from a coalition of fiscal hawks in the House, who announced their own stimulus proposal that centered on corporate tax cuts and other breaks for businesses instead of rebates for taxpayers.

Members of the conservative Republican Study Committee criticized rebates as unnecessary and politically motivated. “If spending was the way to create prosperity, we would never have a recession,” Rep. Paul Ryan of Wisconsin said. “The fear is that we will pass a package that’s good politics but isn’t good policy.”