WASHINGTON -- Congress approved the most far-reaching changes to the nation's campaign finance system since the Watergate scandals on Wednesday, sweeping aside years of gridlock to clear legislation for President Bush's signature.

Bush said he will sign the bill, though he called it "flawed in some areas." Critics attacked the bill as unconstitutional and pledged a swift court challenge.

"With the stroke of the president's pen, we will eliminate hundreds of millions of dollars of unregulated soft money that has caused Americans to question the integrity of their elected representatives," Sen. John McCain, R-Ariz., the bill's leading advocate, said shortly before a 60-40 Senate vote that cleared the measure.

"The reforms passed today, while flawed in some areas, still improve the current system overall, and I will sign them into law," Bush said in a written statement.

The House passed the bill last month on a vote of 240-189. Bush and his team reluctantly began preparing for a signing ceremony as early as next week that will include the bill's sponsors, including his 2000 presidential primary foe McCain.

Spectators in the Senate visitors' gallery broke into applause as the vote was announced, and Sen. Russell Feingold, of Wisconsin, the chief Democratic supporter, smiled broadly as he watched from the rear of the chamber. Reps. Christopher Shays, R-Conn., and Martin Meehan, D-Mass., the leading House sponsors, crossed the Capitol to witness their triumph.

The 60-40 roll call belied years of political combat on the issue, a struggle that launched McCain's rise to national prominence.

"The status quo is not acceptable and today it will end," said Senate Majority Leader Tom Daschle, D-S.D. "The currency of politics should be ideas, not dollars."

After years of delay, Republican opponents offered congratulations to the bill's supporters -- and said they would see them in court.

"I am consoled by the obvious fact that the courts do not defer to the Congress on matters of the Constitution," said Sen. Mitch McConnell, R-Ky., the measure's most prominent Senate critic.

"We have allowed a few powerful editorial pages to prod us into infringing the First Amendment rights of everyone but them," he said, contending the measure would prove detrimental to the political parties.

Under the bill, any challenge would be heard by a three-judge panel in U.S. District Court in the nation's capital. Appeals would go directly to the Supreme Court.

'Soft money' ban

The centerpiece of the bill is a ban on unlimited "soft money" donations to the national political parties, typically five- and six-figure donations made by corporations, unions and individuals.

State and local parties could accept up to $10,000 a year in soft money per donor for voter registration and other party-building affecting federal candidates.

Another key provision would ban the use of soft money to buy "issue ads" within 60 days of an election or 30 days of a primary. These ads are customarily purchased by political parties or outside groups. And while they stop short of expressly advocating the victory or defeat of a candidate, they often are harshly critical.

Individuals would be permitted to donate up to $2,000 to presidential or congressional candidates, a doubling of the present $1,000 limit.

The changes will take effect on Nov. 6, meaning the parties can continue to raise hundreds of millions of dollars in soft money to support candidates in this fall's midterm elections.

There were 48 Democrats, 11 Republicans and one independent in favor of the bill. Opposed were 38 Republicans and two Democrats.

The Senate's vote capped a decade of struggle on the issue.

In 1992 President George H.W. Bush vetoed legislation written by a Democratic-controlled Congress to provide partial public financing for candidates who agreed to limit spending.

In 1994 the House and Senate both passed legislation but couldn't agree on a compromise.

McCain teamed with Feingold beginning in 1995 to try again, joined in the House by Shays and Meehan.

The House passed Shays-Meehan bills twice in the late 1990s over the objections of GOP leaders. But McCain and Feingold were stymied by multiple Republican-led filibusters in the Senate.

That changed after the 2000 elections, when Democrats gained Senate seats, and McCain returned from his presidential campaign with enhanced political standing.

With Daschle playing a key role, the Senate passed a version of the legislation last year. The effort nearly blew up in the House last summer in a procedural fight, but supporters forced the bill back onto the floor last month, and prevailed.

While gridlock persisted on Congress, scandals followed one after the other in politics.

Feingold detailed them in his remarks before a final vote -- the White House coffees and the Lincoln Bedroom sleepovers of the Clinton years; former Vice President Al Gore's visit to the Buddhist temple; revelations that the Chinese military had tried to influence American domestic politics.

Add to that the collapse of Enron, the energy trading company whose top officials were political donors, and even critics said McCain, Feingold, Shays and Meehan had the momentum they needed to prevail.

"I think we have a chance to address this constant scandal-waiting-to-happen," said Sen. Fred Thompson, R-Tenn., shortly before the final vote. "We are making headway I think to do something to reduce the cynicism in this country."

But Sen. Phil Gramm, R-Texas, eagerly lent support to the opponents.

"This bill is blatantly unconstitutional," he said, referring to limitations placed on certain types of donations. The measure is "anti-democratic," as well, he said, and will concentrate power "in fewer and fewer and fewer hands."

Bush, like many conservative Republicans, opposed McCain's bill during the presidential race. He grudgingly embraced it in the end.

Senior advisers reluctantly decided Wednesday that Bush has to stage a bill-signing ceremony because he cannot afford to be labeled an opponent of political reforms.