WASHINGTON — Facing the loss of fellow moderates in the Nov. 7 elections, Republican centrists in the House and Senate are faulting congressional and party leaders for pursuing a political strategy dominated by conservative themes.

Leading moderates say Republicans concentrated on social wedge issues like same-sex marriage while pressing national security almost to the exclusion of popular wage and health policies that could have helped endangered Republicans in the Northeast and Midwest.

"There wasn't an impetus to help develop a political and legislative plan that incorporated the broad umbrella of philosophy in our party," said Sen. Olympia J. Snowe, R-Maine, whom experts expect to be re-elected. "I think they always operated under the wrong assumption that you just appeal to the base and no more than that."

Snowe and other moderates, while holding out hope that most of their counterparts would hang on, were dismayed by the prospect of depleted ranks, saying it could lead to a more polarized Congress.

Two Senate Republicans often found in the small moderate bloc, Lincoln Chafee of Rhode Island and Mike DeWine of Ohio, are in serious jeopardy. Two leading House moderates are retiring, another lost a primary, and at least six others are in difficult re-election fights in Connecticut, New Hampshire, New York, Ohio, Pennsylvania and elsewhere.

The centrists said heavy losses outside strongholds in the South and parts of the West and Midwest could imperil the party's future. They say Republicans cannot sustain a long-term majority unless the party thrives throughout the country.

"There are some people who, because they are so pure and so sure of themselves, they are willing to run the risk of having the Republican Party no longer be national but be more regional," said Rep. Sherwood L. Boehlert of New York, a respected moderate who is retiring. "They think they can maintain their majority as a regional party."

Conservatives say the overall party message was developed to draw the most loyal voters to the polls by emphasizing bedrock principles. The leader of one group that backed conservative candidates in Republican primaries, angering the moderate wing, said some moderates were in trouble simply because they strayed too far, alienating Republicans without attracting Democrats.

"We have people who are certainly well left of the center of the Republican conference on all issues, including economic and growth issues," said the leader, Pat Toomey, a former congressman from Pennsylvania who heads the Club for Growth. "I'm not hoping they lose. But if they do, I think we will be able to recapture those seats with pro-growth candidates who distance themselves from Democrats."

Even conservatives acknowledge that the push did not make it easy for candidates in close races in New England and Ohio.

"It is a real quandary," said Sen. John Cornyn, R-Texas. "It is true that in order to motivate folks there has been an appeal made to turn out our conservatives, which by definition doesn't help those who are not as in tune with the base."

In past election cycles, Republican moderates, like their right-leaning Democratic colleagues in the South, have survived by emphasizing differences with their own party on pivotal issues. Independent voters at home have indicated a willingness to back their lawmakers and draw a distinction between them and the party.

But this year, given the Iraq war, dissatisfaction with President Bush and a series of Republican scandals, some voters no longer seem willing to separate the two.

"It appears we have finally pushed them far enough to vote for the Democratic Party," said Sarah Chamberlain Resnick, executive director of the Republican Mainstreet Partnership. "As a loyal Republican, I think that is scary."

Democrats have also made a concerted effort to unseat vulnerable Republican moderates, which Sen. Susan Collins, another Maine Republican, said was not much of a reward for those who have been most willing to try to work with the opposition party.

"There is no one who has voted more often with the Democrats than Linc Chafee," Collins said. "Yet that didn't stop them from going after him with everything they had. That is a good lesson."

Collins and Snowe noted that although voters indicate a strong desire for bipartisanship, some lawmakers most likely to be punished are the very ones who have reached across the aisle.

Rep. Rahm Emanuel of Illinois, chairman of the Democratic Congressional Campaign Committee, made no apologies for focusing on Republican moderates and said Republicans should blame the party leadership for its hard-right approach.

"They left these guys to fend for themselves in districts that have been trending Democratic," Emanuel said. "What we did was recruit and fully fund our candidates."

Republicans leaning toward the middle on social, environmental and spending matters have been raising the alarm for months, saying the party was missing opportunities to bolster moderate candidates with measures on raising the minimum wage, expanding stem cell research and ethics reform.

But the minimum-wage increase died when it was tied to a move to repeal the estate tax, President Bush vetoed the stem cell measure, and the drive for ethics reform collapsed.

"I don't think the agenda has been particularly helpful," said Rep. Michael N. Castle, R-Del, who said some Republicans had been dismissive of the centrists until the leadership this year was desperate for their votes on major bills.

"I will be the first to say there are those in the Republican Party who feel moderates are essential only in terms of numbers," Castle said.

While Republican moderates are struggling to maintain their numbers, some top Democratic challengers this year are from the more moderate wing of that party, raising the prospect that some Democratic gains will come from the right.

That possibility also gives Republican moderates hope that even if there are fewer of them, they could potentially band with Democrats in the center to influence measures, particularly if the margins between the two parties are thin on Capitol Hill.

"I think," Collins said, "the moderates in both parties could be empowered."