WASHINGTON — For House Republican leaders, passage of wide-ranging spending cuts by a razor-thin margin early yesterday morning may be the easy part. Now they have to reach a compromise with the Senate, which has passed a bill that differs in many ways.

A basic difference is the price tag — the House bill would cut federal spending by $50 billion over the next five years; the Senate's measure cuts $35 billion.

In seeking a compromise, the GOP could find itself caught between two factions of the party: conservatives who complain that spending has grown out of control, and a smaller group of moderates who champion the social programs targeted for cuts.

Also complicating the coming talks are differences between the chambers unrelated to spending. The Senate bill, for example, would authorize energy exploration in Alaska's National Wildlife Refuge; the House version would not.

It is far from certain that the House and Senate can reach an agreement on the first effort since 1997 to slow the growth of federal benefit programs.

"There's a reason" Congress does not try to pass a complex deficit-reduction package every year, House Speaker J. Dennis Hastert, R-Ill., said after the House spending-cut bill barely passed, 217-215. "It ain't easy to do."

Robert L. Bixby, executive director of the Concord Coalition, which lobbies for balanced budgets, said: "The House and Senate are far apart, not just in dollars but in content. ... It is going to be very difficult for negotiators to put them together in a way that doesn't make the whole thing unravel."

As if obtaining a compromise on a spending reduction bill won't be hard enough, looming behind it are different House and Senate tax cut measures.

Passage of both a spending cuts bill and a tax reduction measure is seen as a critical test of President Bush's determination to keep taxes low without adding more to the federal deficit, which was $319 billion for the fiscal year that ended Sept. 30.

The $50 billion in cuts sought by the House bill would be barely more than 0.3 percent of projected federal spending over five years. But Brian M. Riedl, a budget expert at the conservative Heritage Foundation think tank, said making those cuts would be an "important first step to prepare lawmakers for larger reforms next year and after."

Conservatives have vowed to seek spending cuts at least equal to the amounts allocated for reconstruction of the hurricane-damaged Gulf Coast, currently about $62 billion.

The House bill would achieve its cuts in part by trimming benefits provided by Medicaid health insurance for the poor, as well as food stamps, student tuition aid and other programs.

The Senate bill, approved earlier this month, would shield food stamp and Medicaid beneficiaries from cuts. Instead, it would reduce payments to providers of federal benefits, such as pharmacies and drug companies.

The Senate measure also includes a provision opposed by the White House that would cut money for a program to encourage health insurers to participate in the new Medicare prescription-drug benefit.

The House bill contains no changes in Medicare.

The House bill, meanwhile, contains two items not in the Senate version: splitting the 9th U.S. Circuit Court of Appeals into two benches and changing mining laws to permit the sale of public lands in the West for private development. Both provisions face opposition in the Senate.

A fight among House Republicans over spending cuts underscored the challenge facing Congress in trying to reach a compromise bill.

House leaders made concessions to moderates to pick up their votes — such as pledging to seek more home-heating assistance for low-income families. But in doing so, they angered conservatives.

"We have had inordinate success in getting things that are most important to our group," said Rep. Sherwood Boehlert, who joined Republican Rep. Mike Castle of Delaware in negotiations on behalf of a couple of dozen GOP moderates with Hastert and Majority Leader Roy Blunt, R-Mo.

Boehlert, R-N.Y, ticked off concessions that included a reversal of a plan that would have denied 40,000 low-income students free school lunches and cancellation of a plan that would have forced some low-income Americans to make higher co-payments for Medicaid health services.

Some House Republicans objected that their chamber's version of the bill did not include opening the Arctic national wildlife refuge to energy exploration. They have threatened to vote against a final bill emerging from House-Senate negotiations if it does not authorize the drilling.

Reaching agreement on the tax cut bills also is expected to be tricky.

A Senate bill to cut taxes by $60 billion, approved early yesterday, omitted an extension of one of Bush's favorite tax cuts: a reduced tax rate for dividends and capital gains that is to expire in 2008. A proposed $57 billion tax-cut bill in the House, expected to come up for a vote early next month, would extend the lower tax rates for investment income through 2010.

The Senate bill also includes a one-year extension of provisions designed to shorten the reach of the alternative minimum tax, a 1969 provision to prevent the wealthiest taxpayers from sheltering most of their income from the IRS. Under the Senate measure, taxpayers facing the minimum tax would be limited to about 3 million, compared with the 15 million who would otherwise have to pay it.

Whether or not House and Senate Republicans reach agreement, spending and tax cuts are emerging as issues in next year's battle for control of Congress.

"We will be hearing a lot about these votes in the fall of 2006," Bixby said.

Riedl added: "Candidates are already making budget restraint a central issue in their campaigns."