PROVIDENCE, R.I. ? Fresh off their first victory over a Republican incumbent, GOP conservatives seeking party purity on taxes and spending are focused on ousting moderate Republican Sen. Lincoln Chafee, of Rhode Island.

The Club for Growth and its 36,000 members spent about $1 million to help challenger Tim Walberg unseat first-term Rep. Joe Schwarz in Michigan’s Republican primary on Tuesday. The win came despite Schwarz’s support from President Bush and the National Rifle Assn.

Since its inception in 1999, the group has spent millions to help dozens of conservative Republicans win seats in Congress – often at the expense of more moderate party members.

This year, the group’s top priority is defeating Chafee, who angered many Republicans by voting against President Bush’s tax cuts and then casting a write-in vote for the president’s father in the last election. The Club has helped Cranston, R.I., Mayor Stephen Laffey raise hundreds of thousands of dollars to unseat Chafee.

Polls show Laffey trailing far behind the leading Democratic candidate, former Atty. Gen. Sheldon Whitehouse.

The Club’s Web site says that’s fine: “It wouldn’t be much of a loss if a new Democrat senator were elected, as he would vote much the same as Chafee does now.”

Republicans who support the Club say its refusal to compromise gives it credibility.

“They’re not about getting more Republicans elected, they’re about getting real Republicans elected,” said Jerry Stacy, spokesman for Sharron Angle, a Club-endorsed House candidate in Nevada.

Moderate Republicans criticize the Club for targeting incumbents like Chafee instead of going after Democrats.

“I refer to the Club for Growth as the enemy within,” said Rep. Sherwood Boehlert, R-N.Y., whom the Club opposed in GOP primaries in 2002 and 2004.

Economic conservatives founded the Club to encourage the federal government to adopt “pro-growth economic policies.” That includes making the Bush tax cuts permanent, repealing the estate tax, cutting government spending and expanding free trade.