The installation of one of Senator Clinton’s closest political advisers, Harold Ickes, at the helm of the best funded independent political group in Washington could bolster Mrs. Clinton’s chances of winning the White House in 2008, but in the short term, it leaves her with a difficult dilemma.

In the next few months, Mrs. Clinton may have to vote on whether Mr. Ickes’s organization, America Coming Together, will, in essence, be put out of business.

Senator McCain of Arizona and Senator Feingold of Wisconsin are sponsoring a bill that would dramatically restrict the operations of so-called 527 organizations, which are named for the section of the tax code under which they were established. In the last election cycle, some 527 groups raised several million dollars at a time from wealthy donors like investor George Soros. Senators McCain and Feingold denounced the practice, as did President Bush.

According to activists on both sides of the fight, Mr. Ickes, who took the reins at America Coming Together last week, is leading the charge against the legislation, which had its first hearing on Tuesday before the Senate Rules Committee.

“Ickes is out there full guns, on every front he can, fighting this,” said a proponent of the anti-527 bill, Mark Glaze of the Campaign Legal Center. “Raising large amounts of money, primarily in large chunks, is what Harold Ickes does. From his perspective, the bill may be good policy but it threatens his interests.”

One of those whom Mr. Ickes is trying to persuade is the woman who managed Vice President Gore’s presidential campaign in 2000, Donna Brazile.

“Harold Ickes just sent me a big memo,” she said. Ms. Brazile said Mr. Ickes argues that curtailing the funding of 527 groups would hurt voter registration and get-out-the-vote efforts in minority neighborhoods. “He wants me to help lobby the black caucus,” she said.

Ms. Brazile said she isn’t sure the track record of 527 groups indicates they engage in broader outreach than traditional Democratic organizations. “They all had the same battleground state strategy, where two-thirds of the country was left off the political map because no one wanted to put resources into those states,” she said.

Ms. Brazile said the Democratic 527 groups “did a very important job last year,” but that they had the one-time only advantage of a head start over most Republicans, who shied away from supporting 527s because of fears they were illegal.

“Once the FEC declined to regulate, the Republicans kicked our a-. Their campaigns outraised us in the last few months by 6 to 1,” she said.

The veteran political operative said she remains unsure whether she will support the bill to restrict the 527 groups. “I’m really torn,” she said.

Mr. Ickes, who served as a deputy chief of staff under President Clinton and as the campaign manager for Mrs. Clinton’s 2000 Senate bid, did not respond to calls seeking comment for this story.

Mrs. Clinton’s office did not respond to an inquiry about her position on the 527 legislation. In 2002, she voted in favor of the Bipartisan Campaign Reform Act, known as McCain-Feingold.

“Nobody knows whether she’s signed on,” said a Senate staffer who is following the issue closely.

Making the decision even more pointed for Mrs. Clinton is that fact that one of the bill’s co-sponsors is her New York colleague, Senator Schumer.

“It’s a very interesting situation,” said a lobbyist for Common Cause, Celia Wexler. “Certainly, it would be wonderful if Senator Clinton was a cosponsor right now.” There was early pressure on Mr. Schumer to take a stand, because he is a member of the Rules Committee, which is considering the bill.

Under the law, most 527 organizations are not permitted to coordinate their activities with any candidate or political party. Still, a Republican political activist known for grassroots organizing, Morton Blackwell, said if the 527 organizations remain a part of the political landscape, Mrs. Clinton could benefit from having Mr. Ickes at America Coming Together, which spent a record-breaking $78 million on voter registration and turnout efforts in the last election.

“He is generally considered to be in her camp, and it’s logical she would want to have operations that are sympathetic to her in the future,” including in a possible presidential bid, Mr. Blackwell said. “It is possible to do a lot of things and not break the law. It may well be possible among close friends to break the law and never get caught at it.”

A Democratic operative who worked on Senator Kerry’s presidential campaign, Christopher Lehane, said Mr. Ickes’s presence could be helpful as Mrs. Clinton ponders a presidential bid of her own, but only at the margins. “It’s not like Hillary does not have a wide circle of friends,” he said. “This is just simply an additional brick in the wall of what is already a pretty strong, formidable wall.”

So far, the most public opposition to the bill to restrict 527s has come from nonprofit charitable and educational organizations. More than 170 of them are fighting the legislation through an umbrella group called the Coalition to Protect Independent Political Speech.

While the bill’s proponents have decried some of the advertising run by 527 groups in the last election, the coalition of nonprofits said cutting off funds to 527s is not an appropriate response. “The suppression of speech because it is distasteful to some is utterly at odds with American free speech principles,” the coalition wrote in an open letter this week.

The pending bill excludes traditional nonprofits from its reach, but many of those groups have indicated they fear their donor pool could be the next to be regulated.

The new legislation, dubbed the 527 Reform Act of 2005, would make 527 groups follow rules that apply to political action committees, including various caps on individual donations.

Most 527 groups are vigorously opposing the bill behind the scenes, but they have yet to try to persuade the voters on their massive e-mail lists that the legislation should be killed.

In an e-mail to more than 400,000 America Coming Together supporters on Wednesday, Mr. Ickes wrote, “We progressives – young and old – are in for the battle of our lifetime. Are you ready?” However, his only reference to the 527 bill was a bland discussion of the “the changing Federal Election Committee laws regulating 527 organizations like ACT.”

A competing grassroots operation, MoveOn.org, has also kept quiet about the looming legislative fight. Officials with the group did not respond to emails seeking comment for this story.

A spokesman for financier George Soros, who gave nearly $25 million to 527 groups before last year’s election, said he has not decided whether he will back those groups again in the future.

“I think George feels his money was well spent,” the spokesman, Michael Vachon, said. “Whether George is going to write another $1, $5, $10 million to ACT? There are no plans to do that now, but there are no plans not to.”