A rebellion among moderate Republican senators trying to curb tax cuts has thrust the compromise $2.4 trillion budget for 2005 into deep trouble in the Senate.

Seemingly short of the votes they need, Senate Republican leaders said Thursday they had not decided whether to begin debating the measure. "We're working to try to get the votes," said Sen. Rick Santorum (search), R-Pa.

The House used a mostly party-line 216-213 vote Wednesday to approve the fiscal blueprint. It is a modest one-year plan shorn of any long-range policies on deficit-reduction or job creation, in order to minimize controversy. The proposal also has weaker restrictions on future tax cuts than moderate GOP senators want.

Republican leaders hoped the House vote and pressure from Bush administration officials would get Senate GOP moderates to relent.

"I hope senators recognize the importance of helping our nation's families and urge them to act quickly to make sure millions of taxpayers don't get hit with a tax hike," Treasury Secretary John Snow (search) said in a written statement.

Many House moderates heeded their GOP leaders appeal for support on the spending measure. But four of their Senate colleagues — plus moderate Democratic Sen. Ben Nelson (search) of Nebraska — were not as ready to accommodate.

Sen. Susan Collins, R-Maine, on Wednesday became the last of the group to say she would oppose the budget, leaving GOP leaders two votes shy, at least for now, of what they need for approval. The moderates said record federal deficits mean tax cuts should be constrained.

A failure by the GOP-run Congress to complete a budget would be an election-year embarrassment for the party, whose leaders pledged to pass a spending plan to highlight their ability to govern. It is also a slap at President Bush, who has opposed the tax-cut curbs GOP moderates and Democrats want.

Without a budget, it would be harder for Congress to cut taxes and raise the government's borrowing limit later this year.

The budget is a guide for future tax and spending bills. The compromise version, reached in House-Senate negotiations, would pave the way for more modest tax cuts than what Bush proposed.

It would impose constraints on tax cuts for one year, although exempting a single-year $27.5 billion tax bill Congress is expected to pass this year. That measure keeps the lowest 10 percent tax bracket, the $1,000 per child tax credit and breaks for two-income married couples from getting smaller, as scheduled under current law.

Bush proposed a more ambitious tax cutting agenda — nearly $1.3 trillion in tax cuts over the next decade, mostly by making recent tax reductions permanent.

The budget also claims to leave next year's deficit at $367 billion — just below last year's $375 billion record, and $4 billion more than what forecasters expect without the budget's proposed policies. The measure also would bestow big boosts on defense and anti-terrorism programs, with only slight increases for other domestic programs.

The House vote and the apparent impasse in the Senate culminate a two-month standoff between the GOP-led chambers over whether record deficits should require future tax cuts should to be limited. That conflict has clearly angered House leaders.

"We'll do what we can do, and good luck to them," the No. 3 House GOP leader Roy Blunt of Missouri said of the Senate.

In March, Democrats and moderate Republicans forced into the original Senate version a requirement that tax cuts and expanded benefits be paid for with either spending cuts or tax increases for five years.

That passed the Senate. The House version had no such restrictions.

Bush also proposed halving this year's huge deficit — expected to exceed $400 billion — in five years. The compromise congressional plan achieves that goal, but partly because its tax cuts would last only for one year and it lacks a long-range defense buildup.

It also:

_meets Bush's request of $421 billion for defense, 7 percent over this year. There is another $50 billion for wars in Iraq and Afghanistan, of which Bush has so far requested half.

_increases domestic security by 15 percent to $31 billion, while holding remaining domestic programs to $369 billion, $2 billion over this year.