Mr. Abramoff, a major Republican Party fund-raiser who is the focus of a federal corruption investigation in Washington involving gifts to lawmakers, was long among the most generous lobbyists in the capital in directing political contributions to lawmakers who could help his clients.

The money, most of it from Mr. Abramoff's Indian tribe clients and their lucrative casino operations, was eagerly accepted by members of Congress until this year.

But no more. Political strategists working for likely challengers in several 2006 Congressional races have said they intend to publicize the donations, arguing for the ouster of incumbents tied to Mr. Abramoff and his clients.

In announcing last week that they would return money from Mr. Abramoff's clients and his lobbying partners, Senators Conrad Burns, Republican of Montana, and Byron L. Dorgan, Democrat of North Dakota, made clear that they were trying to distance themselves from accusations that they had done favors for Mr. Abramoff in exchange for the donations.

Mr. Burns, who is facing a difficult re-election fight next year in part because of news coverage back home about his links to Mr. Abramoff, called for other lawmakers to return donations from the lobbyist, who is also under indictment in Florida on unrelated fraud charges. "This is an important step that all public officials should take in order to renew the faith" of voters, he said.

Senator Dorgan, the ranking Democrat on the Senate Indian Affairs Committee, said he was returning $67,000.

"I think a lot of voters are beginning to recognize the name Jack Abramoff," said Harry Mitchell, chairman of the Arizona Democratic Party. Mr. Mitchell said in an interview that the disclosures had given the party a clear opportunity to unseat at least one of the state's Republican House members, Representative J. D. Hayworth of Scottsdale.

According to the Center for Responsive Politics, a research group in Washington that monitors the influence of money in politics, Mr. Hayworth was the largest single Congressional recipient of donations from Mr. Abramoff and his family, his associates, his Indian tribe clients and a gambling cruise ship line that he owned, with more than $101,000 going to Mr. Hayworth and his political action committee since 1999. Mr. Hayworth was also a frequent guest in sports skyboxes controlled by Mr. Abramoff and his clients, and at Signatures, a Washington restaurant owned by the lobbyist.

Mr. Mitchell said Mr. Hayworth needed to return donations linked to Mr. Abramoff if he wanted to prove that he was not involved in "all the corruption that's been going on in Washington." In the meantime, Mr. Mitchell said, the party was looking for a strong candidate to challenge Mr. Hayworth in a race that, he said, would now focus in large part on the incumbent's ties to Mr. Abramoff.

Mr. Hayworth's chief of staff, Joe Eule, said in a statement that he did not take Mr. Mitchell's threats seriously and that the congressman had no intention of returning the money.

He said that Mr. Hayworth, co-chairman of the House Native American Caucus, "has been a hero to tribes nationwide" and that it was not surprising that "tribes, including a few formerly affiliated with Mr. Abramoff, have been generous in supporting Mr. Hayworth's political efforts."

The research by the Center for Responsive Politics shows that of the top 25 Congressional recipients of political money linked to Mr. Abramoff, 19 are Republicans and 6 are Democrats. The second largest recipient was listed as House Speaker J. Dennis Hastert of Illinois, with $69,000 in donations.

The Democrats include, tied at No. 16, Senator Harry Reid of Nevada, his party's Senate leader, who received a total of $30,500. Asked if Mr. Reid was considering whether to return the money, his office said in a statement that he was "reviewing the circumstances of the donations."

The top Democrat on the list, who at No. 8 took in $42,500, is Representative Patrick J. Kennedy of Rhode Island, who sits on the House Appropriations Committee, which determines how the federal budget is divided. Sean Richardson, a spokesman for the lawmaker, said that Mr. Kennedy was a founder of the Native American Caucus, that he had a "direct personal relationship with tribes" and that "none of it has anything to do with Jack Abramoff."

Only days before Mr. Burns announced last week that he would return $150,000 in contributions linked to Mr. Abramoff and his partners, his office had insisted that the donations were proper and had already been spent. "There's nothing to return," his spokesman, James Pendleton, said at the time.

The Center for Responsive Politics, which did not include donations from Mr. Abramoff's lobbying partners in its calculations, found that since 1999 Mr. Burns received $49,590 from Mr. Abramoff's Indian tribe clients.

Mr. Burns is widely seen as one of the most vulnerable Republican incumbents in next year's Senate elections; a recent poll by Montana State University showed him with an approval rating of less than 50 percent. News reports in Montana have documented how he took a series of actions favorable to Mr. Abramoff's clients around the time he received large campaign contributions linked to the lobbyist.

Insisting that his actions were never tied to donations, Mr. Burns wrote to Attorney General Alberto R. Gonzales last month, asking that his ties to Mr. Abramoff be reviewed quickly by the Justice Department so he could be cleared of wrongdoing before next year's election.

"I welcome your thorough and expeditious review of this matter so that it may be disposed of officially once and for all and these outrageous and wrongful allegations may be put to rest before we get into the 2006 re-election cycle," Mr. Burns wrote.