A free-market interest group with past financial ties to the House majority leader, Tom DeLay, has heightened tensions inside the Republican Party through an aggressive publicity campaign against fiscal moderates who oppose large tax cuts.

The three-year-old Club for Growth, which received $50,000 from DeLay's political action committee last year, has drawn attacks from the White House, as well as upset Democrats.

Presidential adviser Karl Rove said the group's latest television ads -- which criticized Senators Olympia J. Snowe, Republican of Maine, and George V. Voinovich, Republican of Ohio, for pushing smaller tax cuts than President Bush requested -- were ''stupid and counterproductive and not helpful.''

David Keating, the club's executive director, said his group has no qualms about attacking politicians it considers ''Republicans In Name Only,'' or RINOs. ''We'll challenge any Republicans if they are not free-market oriented, fiscally responsible, and in favor of lower taxes,'' he said.

For the 2004 election cycle, the club plans to raise $20 million -- twice that garnered in the 2002 cycle -- and spend much of that money against fiscal moderates in Republican Senate primaries. Keating said his group is particularly focused on the Pennsylvania Senate race, supporting fiscally conservative Representative Pat Toomey against fiscally moderate incumbent Arlen Specter.

The contretemps set off by the Club for Growth shows how Washington interest groups wield influence on the national political debate, despite campaign finance laws designed to minimize negative advertising by special interest groups.

On Tuesday, the Democratic Senatorial Campaign Committee filed a complaint with the Federal Election Commission, arguing that the Club for Growth ads violate campaign finance laws that prohibit such groups from employing advertising that ''attacks or opposes'' specific candidates. The club has also launched ads criticizing the Senate minority leader, Tom Daschle, Democrat of South Dakota, for opposing the Bush tax cuts.

But the club's president, Stephen Moore, said ads are legal because they focus on an issue, not a candidate. ''The ads are about tax cuts, not the election of Tom Daschle,'' said Moore. He added that the implications of the committee's complaint ''are pretty frightening from a free speech perspective.''

Moore, who calls the club ''the conservative conscience'' of the GOP, founded it in 1999 along with Dusty Rhodes, president of National Review; Ed Crane, president of the libertarian Cato Institute; economist Richard Gilder; and investment banker Larry Kudlow of CNBC's ''Kudlow & Cramer.'' Other backers include Nobel Prize- recipient economist Milton Friedman, former Jersey City, N.J., mayor Bret Schundler, and former GOP gubernatorial nominee Bill Simon of California. The group raises money from 9,500 members for its campaigns.

The group's current focus is tax cuts and supporting supply-side Republicans, but ''the next big dragon to slay is Social Security privatization,'' said Moore.

Last October, DeLay's political action committee, Americans for a Republican Majority, donated $50,000. According to a spokesman for DeLay and the club, that money was used specifically to support Republicans in tight races against Democrats, not to attack moderate Republicans. Stuart Roy, a spokesman for DeLay, said, ''We knew for sure that 100 percent of the money was going to be used to win Republican seats.''

But Sarah Chamberlain Resnick of the Republican Main Street Partnership, a group that supports moderate Republicans, said DeLay's donation was ''unfortunate,'' noting that the representative knew that one of the organization's main missions is attacking moderate Republicans.

The club's aggressive campaign has added to a climate of alienation for many moderate Republicans, particularly in New England. In 2001, Senator James Jeffords of Vermont left the party, expressing concern that it had become too conservative. Soon after the Club For Growth ads were aired, he criticized Bush's tax cuts, commended the Republicans who were working to narrow them, and asked, ''When did standing on principle, speaking your conscience, and representing your constituents become unacceptable in certain Republican circles?''

Constance Morella, a former member of Congress from Maryland and a moderate Republican, said the club's attacks, and DeLay's support of the group, have contributed to a congressional environment where bipartisanship is scorned and Republicans and Democrats are ''afraid to talk to one another.''

The first round of ads attacking Snowe and Voinovich, which debuted April 17, compared the senators to President Jacques Chirac of France, equating opposition to Bush's domestic agenda to opposing the war in Iraq. A second round of ads called to mind John F. Kennedy and Ronald Reagan, arguing that both those presidents cut taxes and created jobs and that Snowe and Voinovich were standing in the way of Bush doing the same.

The Club for Growth said it spent $100,000 on the ads in Maine and Ohio. In Maine, Republican Main Street Partnership responded by spending about $40,000 on ads supporting Snowe. Senator Edward M. Kennedy's office has harshly criticized the use of his brother's name in these ads, sending a letter to the club last week saying that the spots are ''politically irresponsible and grossly inaccurate.''

Christian Potholm, a professor of government at Bowdoin College in Maine, called the ad campaign ''a harebrained scheme to embarrass the president and divide the Republicans.'' Potholm said Maine is divided: about one-third Republican, one-third Democrat, and one-third Independent. With that makeup, Potholm said, a Republican who can't take votes from moderates can't win an election.

On May 6, the club released polling data supporting its contention that both Voinovich and Snowe would be highly vulnerable if they faced a conservative Republican challenger in the primaries.

But Neil Newhouse, a Republican pollster at Public Opinion Strategies, said the surveys were biased. For example, he said, when asking respondents whether they agreed with Bush's or Snowe's position on the tax cut, the club's poll described Bush's stance in much more enthusiastic terms.