A new political weapon known as the "super PAC" has emerged in recent weeks, allowing independent groups to both raise and spend money at a pace that threatens to eclipse the efforts of political parties.

The committees spent $4 million in the last week alone and are registering at the rate of nearly one per day. They are quickly becoming the new model for election spending by interest groups, according to activists, campaign-finance lawyers and disclosure records.

The super PACs were made possible by two court rulings, including one early this year by the Supreme Court, that lifted many spending and contribution limits. The groups can also mount the kind of direct attacks on candidates that were not allowed in the past.

Three dozen of the new committees have been registered with the Federal Election Commission over the past two months, including such major players as the conservative Club for Growth, the Republican-allied American Crossroads and the liberal women's group Emily's List.

FEC records show that super PACs have spent more than $8 million on television advertising and other expenditures, almost all of it within the past month. Groups favoring GOP candidates have outspent Democratic supporters by more than 3 to 1, mirroring an overall surge in spending by the Republican Party and its allies in recent weeks, records show.

The super PACs have "opened the door to the clearest, easiest way to spend unlimited funds on an election," said Trevor Potter, a former FEC chairman who served as general counsel to GOP presidential candidate John McCain in 2008. "This is pretty much the holy grail that people have been looking for."

The new committees are part of a complicated patchwork of fundraising operations that fuel political campaigns. They range from committees formed by individual candidates to the political parties and interest groups. The system relies heavily on political action committees, or PACs, which are mostly used to donate funds to indvidual campaigns and must adhere to strict limits on donations.

But the super PACs, officially known as "independent expenditure-only committees," are free of most of those constraints. The only caveat is that they are not allowed to coordinate directly with candidates or political parties. The groups must disclose their donors, although most have not done so yet because they are so new and will not file their first disclosure reports until mid-October.

Among super PAC spending, more than half has come from American Crossroads, a pro-Republican group founded with the help of former George W. Bush administration adviser Karl Rove. Donations to the group include $400,000 from American Financial Group, a publicly held company, which could make the contribution because of the Supreme Court ruling in Citizens United v. Federal Election Commission. That ruling lifted restrictions on corporate spending in elections.

In two days last week, American Crossroads' super PAC reported spending $2.8 million on ads attacking Democratic candidates, including Rep. Joe Sestak (Pa.), Jack Conway (Ky.) and Senate Majority Leader Harry M. Reid (Nev.). "Harry Reid," one ad intones, "extremely out of touch with Nevada."

The super PAC is just one part of the American Crossroads operation, which also includes a nonprofit advocacy arm called American Crossroads GPS that does not have to disclose its donors under U.S tax laws. Overall, American Crossroads says it has raised about $32 million, divided evenly between its super PAC and nonprofit arms.

"There are some donors who are interested in anonymity when it comes to advocating for specific issues," spokesman Jonathan Collegio said.

Indeed, donor disclosure is the main reason that some trade groups, unions and other organizations might limit their use of super PACs, experts said.

Otherwise, the model offers a number of clear advantages.Unlike regular political action committees, there are no limits on how much money can be raised or spent. And unlike some other types of committees, super PACs can explicitly urge voters to oppose or support a candidate in an election.

"For people who want to get involved in the election and don't mind doing it openly and transparently, this is the route they're going," said Brett Kappel, an election lawyer at the law firm Arent Fox. "The people who are more bashful are giving to nonprofits."

The rise of super PACs is just one reason that 2010 is shaping up to be a record-breaker for a midterm election. Interest groups and political parties have reported more than $104 million in independent spending, and that does not include tens of millions more spent by groups that do not have to report advertising to the FEC.

The super PAC model emerged with little fanfare this summer from a pair of FEC advisory opinions, which were issued in response to inquiries from the Club for Growth and another group, Commonsense Ten, which supports Democrats. The FEC said the super PACs were allowed because of the Citizens United decision and a subsequent appeals court ruling, which struck down limits on individual contributions to independent groups.

David Keating, the Club for Growth's executive director, said old rules that were being applied to independent groups - including limits on explicit appeals to both donors and voters - were awkward and forced the organizations to be vague about their intentions.

"What's really liberating about this particular type of organization is that you can actually talk to people honestly about what you want to do," said Keating, who is also head of SpeechNow.org, the conservative group involved in the appeals court case. "Raising money is also a lot easier and more on the up-and-up for everyone involved."

President Obama and other Democrats have railed against the Citizens United ruling because they say it could unleash a tide of corporate and special-interest money into the political process. Since the ruling, Democrats have tried to impose disclosure requirements for companies, unions and others - much like those now required for super PACs - but have been blocked by Republicans.

In addition to American Crossroads, leading super PACs include the Club for Growth ($1.9 million); Women Vote! from Emily's List ($400,000); and the Patriot Majority ($700,000), which was formed by a Democratic strategist to counter the tea party movement. Several major unions have formed super PACs in recent weeks, along with the Texas Tea Party Patriots and other conservative groups, records show.

The number of new entrants is expanding almost daily. Last Tuesday, a new group called We Love USA registered its super PAC with the FEC, listing Nancy Watkins of Tampa as treasurer. Three days later, she filed notice that the group had made its first expenditures, totaling $33,000, for an outdoor media campaign against Rep. Ron Klein (D-Fla.).

Watkins did not respond to a telephone message seeking comment. The Klein campaign, which is fighting a tough race in South Florida against GOP candidate Allen West, said it had never heard of Watkins or the We Love USA PAC.

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