Republicans expect a close House vote on legislation that would put contribution limits on the nonprofit political groups that proliferated during the 2004 presidential election, chiefly to the benefit to Democrats.

The legislation, which could come to a vote late Wednesday, would require groups known as 527s — made famous by the multimillion-dollar contributions of liberal businessman George Soros and the anti-John Kerry Swift Boat Veterans for Truth — to register as political committees and abide by the same contribution limits as those committees.

In an unusual turnaround, clean government groups have joined Republicans in backing the bill while some conservative organizations are allying with Democrats in opposing it.

The measure, if it passes, would give lawmakers returning home for the two-week Easter recess a way to show they are doing something about money in politics. The Senate last month passed legislation aimed at reducing the unhealthy influence of lobbyists on the lawmaking process, but the House lobbying bill isn't expected to be ready until after the recess.

The 527 groups, named for the section of the tax code that describes them, are unincorporated political organizations currently exempt from regulation by the Federal Election Commission. They became prominent after Congress passed the 2002 campaign finance law that banned federal candidates and the national parties from accepting unlimited donations from individuals, unions and corporations.

Rep. Christopher Shays, R-Conn., who with Rep. Marty Meehan, D-Mass., sponsored both the 2002 act and the 527 bill, argued before the House Rules Committee Tuesday that 527s had become a "huge loophole" in the effort to control campaign spending. He said that in the 2004 election just 25 wealthy individuals had contributed $142 million to the get-out-the-vote and political advocacy activities of such groups.

But Democrats, who overwhelmingly supported the 2002 act, are generally against the Shays bill, charging that Republicans are trying to dry up a source of income for groups that in 2004 strongly favored Democratic causes.

"There is no doubt that this is a targeted bullet at what the Republicans perceive to be their enemies," said House Democratic Whip Steny Hoyer, D-Md.

Democrats argued it was unfair to restrict 527s and not other tax-exempt groups that could become channels for political contributions. Among those are business groups, such as chambers of commerce, that might tend to support Republican causes.

But several groups that usually side with Democrats on campaign finance issues voiced strong support for the 527 bill.

The Campaign Legal Center, Common Cause, Democracy 21, the League of Women Voters, Public Citizen and U.S. Public Interest Research Group wrote lawmakers that the bill was "necessary to prevent 527 political groups from spending unlimited soft money on campaign ads and partisan voter mobilization efforts to influence federal elections."

But David Keating, executive director of the conservative Club for Growth, said the bill was "politically stupid" for Republicans and "misguided because I don't think it will help Republicans" and may lead to controls on other, more friendly groups.

Rep. Mike Pence, R-Ind., a leader of House conservatives, also warned of "whack-a-mole in American politics," where Congress has to keep going after the latest source of political funding.

Pence was pushing amendments to the bill that would remove the aggregate limit on contributions an individual can make to federal candidates and allow parties to spend unlimited amounts of regulated hard money on their own candidates, even when they coordinate such spending with the candidates.

But Common Cause and the other advocacy groups strongly opposed Pence's proposals, saying they would gut campaign finance laws. Shays said that if the Pence proposals are incorporated, "then the whole bill dies.