WASHINGTON -- The Senate yesterday narrowly defeated a measure that would have made it harder to approve future tax cuts, handing a significant budget victory to President Bush.

On a vote of 50-50 -- one vote shy of the majority needed -- senators rejected a "pay-as-you-go" provision that would have required tax cuts to be paid for by reductions in spending and for spending increases to be paid for with new tax revenue.

The provision, co-sponsored by Sens. George Voinovich, R-Ohio, and Russell Feingold, D-Wis., could be waived if 60 senators voted to do so, a challenging legislative hurdle.

The vote on the provision came as the Senate worked its way through a mountain of amendments to a $2.6 trillion blueprint for next year's federal budget. The House is working on its version of the budget this week, and both chambers hope to complete work tomorrow, when lawmakers plan to adjourn for a two-week recess.

During yesterday's Senate debate, supporters of the "pay-as-you-go" amendment argued that it is the only way to contain spiraling federal deficits. Opponents contended that tax cuts stimulate the economy, and shouldn't be held to the same strictures as spending.

"If we pass this amendment, this is really a tax increase," said Sen. Trent Lott, R-Miss., noting how difficult it would be to get the 60 votes needed to waive the "pay-as-you-go" provision. "The problem is not tax cuts; the problem is that we can't control our insatiable appetite for spending."

Sen. Charles Grassley, R-Iowa, agreed that the proposal was a "stealth tax increase" that would make it harder to extend the tax breaks that Bush pushed through Congress in 2001 and 2003.

Voinovich, however, said the "pay-as-you-go" provision would help Congress "enforce fiscal responsibility" by forcing lawmakers who want tax cuts or spending increases to figure out how to pay for them.

"How can any of us stick to this tough budget that we have and at the same time vote to extend tax reduction?" he asked.

Under the congressional budget process, lawmakers are supposed to approve a blueprint for the next year's federal spending in the spring. The idea is to set targets and leave specific decisions on how to spend the money to separate votes later in the year.

Last year, however, Congress failed to pass a budget blueprint because the Senate passed a "pay-as-you-go" provision, and the House refused to go along with it, leading to a legislative stalemate.

Bush and Republican congressional leaders were determined to avoid a repeat of that process this year. Supporters of "pay-as-you-go," meanwhile, were heartened when Voinovich, who opposed the provision last year, changed his mind and joined four other Republicans in supporting it.

After yesterday's vote, Voinovich spokeswomen Marcie Ridgway said her boss was "disappointed" that the provision was defeated. But she added: "The vote was a lot closer than we had anticipated, and we think it shows the rising concern for the issue."