The Republican-led U.S. House of Representatives passed a bill on Wednesday to crack down on independent political groups that spent nearly a half-billion dollars in the 2004 election, most of it trying to help Democrats.

The measure would impose limits on individual contributions to those groups and require them to register with the Federal Election Commission. On a largely party-line vote of 218-209, the House sent the bill to the Senate where it faces an uncertain fate.

Senate Minority Leader Harry Reid, a Nevada Democrat, said Congress may want to examine campaign financing in advance of the November congressional elections — but it should not zero in on just one component.

“If we’re going to take a look at everything here and have a real good, in-depth look at campaign financing again, I’m happy to do that, but not cherry-pick what somebody doesn’t like,” Reid said.

While Republicans control the Senate, holding 55 of 100 seats, Democrats could try to stop the bill with a procedural roadblock.

Independent political advocacy groups became increasingly popular after Congress passed a campaign finance bill in 2002 designed to reduce the influence of money in politics by banning unlimited corporate, union and individual contributions to national parties.

But there are no limits on individual donations to independent political groups known as 527s, named for the part of the tax code that regulates them.

“All we are trying to do is close a loophole,” said Rep. David Dreier of California, a member of the Republican leadership.

House Minority Whip Steny Hoyer, a Maryland Democrat, denounced the bill, saying, “They (Republicans) are trying to gag their opponents, and further empower their supporters.”

Many conservative groups, including Club for Growth and the National Taxpayers Union, broke ranks with Republicans and opposed the bill. They charged it would reduce free speech.

Several campaign-reform groups, including Public Citizen and Common Cause, back the measure.

In the 2003-04 election cycle, independent advocacy groups active in federal elections raised $426 million — $321 million by pro-Democratic groups and $104 million by pro-Republican ones, according to the Campaign Finance Institute.

The House-passed bill would impose an annual limit of $5,000 for an individual to give to a group for its federal election activities.

Those groups are already prohibited from coordinating activities with candidates or political parties.

Philanthropist George Soros gave millions of dollars to advocacy groups in a failed 2004 bid to unseat President George W. Bush in 2004.

A conservative advocacy group, Swift Boat Veterans for Truth, made its mark by challenging the war record of Democratic presidential nominee John Kerry.

Rep. Marty Meehan, a Massachusetts Democrat, joined Rep. Christopher Shays, a Connecticut Republican, in sponsoring the bill to clamp down on those groups. They were chief sponsors of the 2002 campaign finance measure as well.

“Congress today affirmed that 527 groups have a right to organize and to be involved in elections, but that they should have to play by the same rules as everyone else,” Meehan said.

Just seven Democrats joined 211 Republicans in voting for the bill, while 190 Democrats, 18 Republicans and one independent opposed it.