Washington ? Republicans conceded defeat Tuesday and the Senate got ready to approve legislation to curb the hundreds of millions of dollars of unregulated “soft money” that has flowed into election campaigns in the past decade.

Sen. Mitch McConnell, R-Ky., who for years has helped fight passage of campaign finance legislation, acknowledged that this time he would not prevail. “The opponents of this bill are ready to move on,” he said.

The two sides agreed late Tuesday that they would move at 1 p.m. today to shut off debate, an action that requires 60 votes. If that clears, as expected, a vote on final passage would come later this afternoon.

The legislation, passed by the House last month, would then go to the White House. President Bush, while never enthusiastic about the measure, has indicated he would sign it.

“It’s a very fine moment,” said Sen. John McCain, R-Ariz., the partner of Sen. Russ Feingold, D-Wis., in a seven-year odyssey by the two to change the way money is raised and spent in national elections.

McConnell said that, following passage, he would move quickly to challenge portions of the bill in court. Opponents say that restrictions on campaign contributions violate First Amendment free-speech rights.

The measure, championed in the House by Reps. Christopher Shays, R-Conn., and Martin Meehan, D-Mass., 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 decadelong 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.