Supporters of a campaign finance bill on the House floor have agreed to leave current free-spending rules in effect until after this fall's election, rather than implement them 30 days after the bill is signed. But their efforts to get the bill passed still may be doomed.

House Republicans on Wednesday offered several alternatives aimed at undercutting support for the legislation aimed at removing millions of unregulated dollars from political campaigns.

Lawmakers are voting on a bill Wednesday that would update campaign finance rules created following President Nixon's resignation after the Watergate scandal. The final vote is not expected until midnight or later.

The Shays-Meehan bill, named after sponsors Rep. Christopher Shays, R-Conn., and Rep. Marty Meehan, D-Mass., calls for a ban on soft-money donations from corporations, unions and individuals that are used by national parties. State and local party organizations still could raise soft money in amounts up to $10,000, but the money could not be used for political ads.

The bill also prohibits "issue ads" financed by corporate or union money within 60 days of a general election or 30 days of a primary. The ads don't mention candidates by name but are often used as attacks in the name of voter education.

In a concession to the National Association of Broadcasters, supporters of the bill said they would agree to allow a vote on an amendment that would strip out a requirement that television stations sell certain political advertising at a highly preferential rate.

Shays-Meehan supporters also agreed to double to $2,000 the current hard-money contribution that individuals can make to House candidates, bringing it in line with the $2,000 limit in the Senate bill. This would also raise hard-money contribution limits for candidates facing millionaire opponents who finance their own campaigns.

Opponents of Shays-Meehan — led by the Republican House leadership — said the soft-money ban would seriously weaken national parties by forcing contributors to seek different avenues to press their political agendas. Opponents insist the limits on issue ads are unconstitutional infringements of free-speech rights.

They have planned a series of 10 amendments, including a ban on soft money for state and local committees as well for the national parties, in an attempt to kill support for the bill. The provision was part of an earlier version of the Shays-Meehan bill, but now is gone.

Rep. Bob Ney, R-Ohio, is offering a stronger version of Shays-Meehan that passed in 1998, arguing that supporters of Shays-Meehan should go all the way if they mean to reform campaign financing.

"I'm going to give people the opportunity to stay honest on this issue," Ney said.

But Ney actually opposes campaign finance reform and has said that the bill is "clearly unconstitutional." Sen. Mitch McConnell, R-Ky., said he would support taking the case all the way to the Supreme Court.

Shays-Meehan supporters say Republican attempts to add "poison pill" amendments are a last-chance effort to kill the bill during a House-Senate conference that would be necessary before the two versions of the bill could go to the president. The Senate passed a similar version, sponsored by Sens. John McCain, R-Ariz., and Russ Feingold, R-Wisc., last year on a 59-41 vote.

President Bush has not joined directly in the intense lobbying on campaign finance but has told House Republican leaders, who oppose Shays-Meehan, that they can't count on his veto if the bill reaches his desk. White House spokesman Ari Fleischer said Wednesday that both major bills pending before Congress would "improve the system in varying degrees, consistent and inconsistent with the president's principles."

"I want to sign a bill that improves the system," Bush said Wednesday, without committing to signature or veto. Bush said he thought the bill's implementation could be put unto effect this year.

Shays-Meehan received more than 250 votes in the 435-member House in 1998 and 1999, when it died in the Senate, but the vote this time is expected to be close.

"There's no longer any place to hide," said Rep. Thomas Reynolds, R-N.Y. "It's going to be settled right in the House of Representatives."

The Associated Press contributed to this report.