The Senate approved landmark legislation yesterday to reduce the influence of big money in political campaigns, capping a fierce, six-year struggle that catapulted Sen. John McCain to national prominence.

The 59-41 vote sent the measure to the House, where a tough fight is expected even though similar bills have been approved twice in recent years. Beyond that, President Bush has not said definitively whether he will sign the bill, and, if the measure is approved, a court challenge to its constitutionality is a certainty.

"He"ll look at it when it reaches his desk. It"s still going through the legislative process," said White House spokesman Scott McClellan.

Supporters hailed the Senate"s action as a signal that campaign finance laws are likely to be changed for the first time since the Watergate era. Passage will "put a lasting mark on the record of democracy," said Sen. Russ Feingold of Wisconsin, the leading Democratic supporter.

"I asked at the start of this debate for my colleagues to take a risk for America," said McCain a few moments before the roll was called. "In a few minutes, I believe we will do just that. I will go to my grave deeply grateful for the honor of being part of it."

Not everyone was pleased with the outcome.

"The bill is fatally unconstitutional" said Sen. Mitch McConnell (R-Ky.), who fought to the end against a bill he has long opposed as an infringement on free speech. In addition, he said, "The underlying theory is that there is too much money in politics, in spite of the fact that last year Americans spent more on potato chips than they did on politics."

A group of more than 60 lawyers form around the country have published and circulated a letter through the Brennan Center of Justice at New York University claiming that the bill is indeed constitutional.

University of Oregon Prof. Garrett Epps was one of the law professors to sign the letter. He said that a former Supreme Court ruling on Buckley v. Valeo established a precedent for restricting the amount of money a person can donate to a campaign.

But other provisions will tangle up the bill, Epps said. The First Amendment issue may be brought up in terms up restrictions on issue advertising and required disclosure from advertisers.

Epps said there is no way to know how the court will rule.

"There are some real consequences to the bill, but they can be fixed," he said.

The legislation would ban so-called soft money, typically five- and six-figure contributions to political parties by unions, corporations and individuals. Republicans and Democrats combined took in nearly $500 million in such funds over the last two years.

It also would ban certain types of broadcast advertising close to an election. The provision, attacked by McConnell and others as unconstitutional, is an attempt to stop the flood of "issue ads" by outside groups that skirted current legal restrictions by avoiding the direct advocacy of a candidate"s election or defeat.

No date has been set for House consideration of the issue, but supporters have said they hope for a vote later this spring. Longtime critics such as GOP Whip Tom DeLay of Texas have announced plans to try and defeat the bill, and even some Democratic supporters appear to be having second thoughts.

Epps said he thinks the bill will pass the House. "There will be a big fight in the House, but all these people have to be re-elected in a year and a half," he said.

"They don"t want to appear against campaign finance reform."

But Epps said he"s not sure that the bill will become law.

"What George Bush is going to do is anybody"s guess," he said.

House Minority Leader Dick Gephardt (D-Mo.), who has supported previous versions of the bill, recently told reporters he favors no change in the contribution limits to candidates and parties, for example.

Senate Democratic Leader Tom Daschle expressed similar concerns, but ultimately accepted an increase and played a pivotal role in keeping support for the measure from eroding.

While Watergate prompted the last major overhaul of campaign finance laws, McCain"s involvement in the Keating Five scandal of the early 1990s he was not cited for any wrongdoing helped spark his interest in the issue.

A furor over fund-raising practices in President Clinton"s 1996 re-election campaign, including Lincoln Bedroom sleepovers and White House coffees with the president for high-dollar donors, gave McCain fresh fodder.

He showed a willingness to clash with his GOP colleagues, often in acerbic terms, and made the ban on soft money into the centerpiece of his bid for last year"s Republican presidential nomination. He stunned the party establishment when he won the leadoff New Hampshire primary 13 months ago, and later displayed an ability to attract the support of millions of independent voters.