The hard-hitting videos, mocking blog posts, and critical issue-by-issue analyses posted on a Web site about Senator Santorum of Pennsylvania might lead some visitors to conclude that the site’s purpose is to undermine the Republican senator’s uphill re-election bid. Not so, according to a disclaimer on the home page of www.santorumexposed.com, which is run by a left-leaning political group, the Lantern Project.

“Contributions to the Lantern Project will neither be used to support or oppose the election of a clearly identified federal candidate nor to influence federal elections,” the site says.

“How can they suggest they’re not advocating for a candidate?” a spokeswoman for Mr. Santorum, Virginia Davis, asked. “It’s absolute hypocrisy.”

The seeming dissonance arises from the murky arcana of campaign finance law and legal ambiguities exploited by so-called 527 organizations, such as the Lantern Project, which raised almost $1 million from labor unions and Democratic donors through the first half of this year.

During the 2004 campaign, other 527 groups, such as the Media Fund and Swift Boat Veterans for Truth, spent more than $100 million on similar efforts to undercut President Bush or his Democratic opponent, Senator Kerry of Massachusetts.

A former member of the Federal Election Commission, Scott Thomas, said the 527 groups’ implausible claims not to be seeking to influence elections while running ads clearly aimed at doing just that are the logical result of the commission’s failure to issue easily understood regulations about what is and is not permitted.

“There’s going to be an awful lot of massaging of language this year, first by the political people, and then by the legal people,” Mr. Thomas said in an interview. “I anticipated that this is exactly where you’d end up.”

The Lantern Project Web site and the television ads the group has run criticizing Mr. Santorum are no tougher than the attacks mounted by the Swift Boat Veterans and MoveOn.org in 2004. However, campaign finance specialists said the Lantern Project is pushing the legal envelope by soliciting donations on its Web site with the line “contribute today and help us expose Rick’s radical agenda.”

Mr. Thomas, a Democrat, said the solicitation falls into “a very, very gray area.”

While the Federal Election Commission traditionally has focused on the minutiae of ads taken out by political groups like 527s, the commission has recently begun to give closer scrutiny to how organizations raise their money.

In 2004, the commission indicated it planned to pursue 527 groups whose pitches for money talked about supporting or opposing a candidate’s election. However, the commission said it would not look at whether a plea for funds came in the midst of a hard-fought campaign, nor at any “implied meanings or understandings” of the language used.

Last year, the commission filed suit against a Republican-supported 527 group, the Club for Growth, on the grounds that its solicitations crossed the line by suggesting that donations would help defeat or elect specific candidates.

The Club for Growth is fighting the complaint in court and contends that the government is seeking to infringe on the group’s First Amendment rights.

In addition, a Washington newsletter, Money & Politics Report, disclosed last year that federal regulators issued subpoenas to “many donors” to 527 groups. Campaign law attorneys said it is highly unlikely, but theoretically possible, that the Federal Election Commission would bring enforcement proceedings against a donor who gave to a 527.

The 527 groups get that name from the section of the tax code under which they are organized.

Efforts to contact a spokesman for the Lantern Project were unsuccessful. A Democratic activist who spoke on behalf of the group last year, David Stone, recently became the head of public affairs for Columbia University. He said he could no longer comment on the organization’s affairs.

A political consultant involved with the group, Joseph McLean, referred questions to two other Democratic strategists, Celia Fischer and Alicia Alexion. They did not return calls yesterday seeking comment for this article.

Two fund-raisers for the Lantern Project, Susan Torricelli and Dan Wofford, have personal ties to prominent Democrats. Mr. Wofford is the son of a former senator from Pennsylvania, Harris Wofford. Ms. Torricelli is the ex-wife of a former senator and longtime congressman from New Jersey, Robert Torricelli.

The Santorum Exposed site contains a video clip in which Mr. Santorum claims, incorrectly, that Barbra Streisand is the Lantern Project’s largest donor. She gave $2,500 last fall.

In fact, the group’s largest donor is the Service Employees International Union, which gave $250,000. Other unions kicked in about $150,000.

Two New Yorkers, Lewis Cullman and Robert Sillerman, each chipped in $100,000 for the anti-Santorum effort.

The Lantern Project is far from the largest 527 to make waves this election cycle. In the past month, a Texas homebuilder, Bob Perry, poured $5 million of his money into a new 527 organization, the Economic Freedom Fund. It is already advertising against incumbent Democrats in tight re-election races, including Rep. Alan Molhollan of West Virginia and Rep. Jim Marshall of Georgia.

In 2004, Mr. Perry gave about $4.5 million to a group that pilloried Mr. Kerry, the Swift Boat Veterans for Truth.

A prominent Democratic activist, Harold Ickes, recently moved to counter the GOP efforts by creating a new 527 group that will seek as much as $25 million, the September Fund.

Mr. Bush’s campaign brought two lawsuits in 2004 seeking to shut down the 527 groups, which the president said should not exist. Ms. Davis, the spokeswoman for Mr. Santorum, said she did not know whether the senator thought 527 groups should be allowed to run ads with money raised from unlimited donations. In an interview with the Pittsburgh Post-Gazette, Mr. Santorum said of the organizations, “Right now, they’re legal.”

One twist in the law that could aid the senator is that the prevalence of union money behind the Lantern Project means it may have to curtail its advertising between now and the election. Corporate and union funds cannot be used to finance television and radio ads mentioning a candidate within 60 days of a general election.

The project’s latest ad, painting Mr. Santorum as a lackey of Mr. Bush and Defense Secretary Rumsfeld, is posted only on the Web.