After seven years of successfully blocking campaign finance reform, opponents of the bill admit that the most sweeping changes since the 1970s to the way political campaigns are paid for will now pass.

The two sides agreed late Tuesday that they would move at 1 p.m. Wednesday to shut off debate, an action that requires 60 votes. If that clears, as expected, a vote on final passage would come later that afternoon for legislation that will ban unlimited "soft money" contributions to national political parties and restrict broadcast ads by outside groups in the final weeks of an election campaign.

The legislation, passed by the House last month, will then go to the White House where President Bush has indicated he would sign it despite some misgivings about the package — including the fact that at the last minute, lawmakers postponed implementation of the reforms until after this fall's election.

"It's a very fine moment," said Sen. John McCain, R-Ariz., who co-sponsored the legislation with Sen. Russ Feingold, D-Wis.

Sen. Mitch McConnell, R-Ky., who for years fought passage of the bill, acknowledged that it was no longer time to fight the bill on the Senate floor.

"As someone who has fought for many years to defeat this bill, it is clear that that position is not going to prevail," McConnell said. "The opponents of this bill are ready to move on."

Opponents have promised for years that if it came to this they would still challenge the changes in court as unconstitutional restrictions on free speech in the form of political spending. McConnell had said that following passage, he would move quickly to challenge portions of the bill in court.

The measure, championed by Reps. Christopher Shays, R-Conn., and Martin Meehan, D-Mass., in the House, would ban corporations, unions and individuals from making unregulated "soft money" donations to the national political parties. For the 2000 election the two parties took in nearly $500 million in such donations, up from $86 million in the 1992 election.

The bill also doubles to $2,000 what an individual can make in regulated "hard money" contributions to an election campaign each year.

And it restricts, in the final 30 days of a primary or 60 days of a general election, those broadcast "issue ads" aimed at supporting or attacking a candidate.

It would be the first major revision in campaign finance law since the post-Watergate year of 1974, and culminates a decade-long battle to do something about soft money, an outgrowth of loopholes in laws from 1907 and 1947 that bar corporations and unions from direct financial involvement in elections.

Feingold, in a floor speech Monday, said eliminating soft money was not a panacea, but "it will end a system of unlimited donations that has blatantly put political access and influence up for sale."

Congress has been trying for the past decade to overhaul the system. In 1992, President George H.W. Bush vetoed a more extensive bill that would have offered partial public financing to congressional candidates who agreed to limit spending. In 1994, the House and Senate both passed legislation but couldn't agree on a common bill. The House passed Shays-Meehan bills twice in the late 1990s but McCain and Feingold couldn't get their version through the then GOP-controlled Senate.

The measure was given a big boost earlier this year with the collapse of energy giant Enron Corp., which critics say lavished campaign contributions on both Republicans and Democrats to gain access to Capitol Hill and influence policy.

McCain said former Vice President Al Gore's visit to a fundraiser at a Buddhist temple, and McCain's championing the cause during his unsuccessful bid for the Republican presidential nomination in 2000 set the stage for passage this year.

McConnell, however, said the bill was more difficult to defeat this time around because its supporters had significantly narrowed its focus to banning soft money for the national parties. State and local parties can still receive up to $10,000 a year per donor in soft money each year for get-out-the-vote and other non-electioneering issues.

He added that Bush's decision to stay on the sidelines and not come out against the legislation made it more difficult to fight. "If the president had indicated an antipathy it certainly would have made it easier to defeat it," he said.

Fox News' Carl Cameron and The Associated Press contributed to this report.