ORLANDO, Fla. — Seeking any slight advantage in their effort to avoid losing control of Congress, Democrats are working behind the scenes in a number of tight races to bolster long-shot third-party candidates who have platforms at odds with the Democratic agenda but hold the promise of siphoning Republican votes.

The efforts are taking place with varying degrees of stealth. And in many cases, they seem to hold as much risk as potential reward for Democrats, prompting accusations of hypocrisy and dirty tricks from Republicans and the third-party movements that are on the receiving end of the unlikely, and sometimes unwelcome, support.

In California, Republicans have received recorded phone calls from a self-proclaimed but unidentified "registered Republican" who says she is voting for the American Independent Party’s candidate for a House seat, Bill Lussenheide, not for the incumbent Republican, Mary Bono Mack. The caller says she is voting that way because "it’s time we show Washington what a true conservative looks like."

The recording was openly paid for by the Democratic candidate for the seat, Mayor Steve Pougnet of Palm Springs.

In Pennsylvania, the Democratic candidate for a suburban Philadelphia House seat, Bryan Lentz, admitted this week that his volunteers helped Jim Schneller — a prominent skeptic of President Barack Obama’s citizenship — collect petitions to run against Lentz and his Republican opponent, Pat Meehan.

In Nevada, conservative radio listeners have heard an advertisement promoting the Senate campaign of a "Tea Party of Nevada" candidate, Scott Ashjian. The ads also criticize Sharron Angle, the Republican nominee and favored candidate of the actual Tea Party movement in the race for the seat of Sen. Harry Reid, the Democratic majority leader.

The ad was sponsored by a group backed by unions and casino and mining companies supporting Reid.

Nevada is one of several states, including Florida, where "Tea Party" political committees have appeared on ballot lines without the knowledge or support of leading Tea Party activists, who have generally chosen not to support third-party candidacies. And in most of those cases, local bloggers, reporters and lawyers have traced connections back to local Democrats, drawing a number of lawsuits, complaints and, in a couple of cases, admissions of involvement.

"It is one of the dirtiest moves," said Rep. Kevin McCarthy of California, a vice chairman of the National Republican Congressional Committee. "It’s not as though the Democrats are playing to compete against the third party — they’re helping to build the third party up to make those votes not count."

Calling it "a concerted effort," McCarthy added, "In congressional races, it could steer the tide for the majority."

In response to questions about whether the efforts were being coordinated on a national level, the Democratic National Committee said in a statement, "Republicans have no one to blame but their own ideological intolerance for the bloody civil war on their side."

Stealth support for third-party candidates who have the potential to cut into the other side’s votes is a time-tested political tradition for both parties.

But this year’s efforts are striking for the potency of the grass-roots movement that Democrats are trying to use to their advantage — that is, the Tea Party — and for the sometimes brazen nature of the attempts.

Pougnet, the Democrat running for Bono Mack’s congressional seat in Palm Springs, openly discloses his sponsorship of the telephone calls and mailings he is directing to conservative voters labeling Lussenheide as "the Tea Party candidate" and Bono Mack as a "raging liberal" by comparison.

"It’s the strangest thing I’ve ever seen," Bono Mack said. "It’s desperate, and I think the voters see right through it."

Pougnet’s campaign manager, Jordan Marks, said, "There’s nothing wrong with pointing out to voters who are more conservative that there’s a more conservative alternative on the ballot."

In other efforts, Democrats have tried to keep a lower profile, although they have not always succeeded.

In Michigan, local Republicans and Tea Party activists were immediately suspicious when a "Tea Party" ballot line appeared with candidates running for two competitive House seats and several state offices. The ballot line was thrown out on a technicality last month, but only after a series of blog and newspaper reports uncovered the hidden hand of two Oakland County Democratic officials. Both men resigned.

Lentz’s admission this week that his supporters had a role in placing Schneller on the ballot in the Pennsylvania House race followed months of suspicion that Lentz was somehow involved. He had avoided questions until this week, when he told the editorial board of The Delaware County Daily Times, "If somebody’s already made the decision to run, I didn’t think that ‘helping’ with the process of signature petitions was improper."

Here in Florida, local Republicans and grass-roots Tea Party activists continue to press the case that "Tea Party" candidates on the ballot are stalking horses for Democrats — an assertion that Democrats deny.

Polls and independent analysts suggest that the incumbent Democrat in Orlando, Rep. Alan Grayson, a firebrand liberal whose defeat is eagerly sought by conservatives, faces an uphill fight to keep his seat in what has been a bitterly fought campaign against his Republican rival, Daniel Webster. But the candidate running on the "Tea Party" ballot line in Orlando, Peg Dunmire, could prove pivotal if Grayson is to pull off a squeaker.

The "Tea Party" in Florida was formed and registered with the state in August 2009 by an Orlando-area lawyer, Frederic B. O’Neal, with help from a longtime client, Doug Guetzloe, an activist, radio host and Republican operative in a running feud with his party, who has earned a colorful reputation as a political trickster. (On Friday, Guetzloe was sentenced to 60 days in prison for a misdemeanor campaign violation relating to an anonymous political flier he sent four years ago, but his sentence does not start until after the election.)

Tea Party activists in the state said they were flabbergasted to learn of the existence of a "Tea Party" ballot line and Guetzloe’s involvement with it.

"I didn’t know who the heck these people were," said Everett Wilkinson, a grass-roots activist who has tangled with Guetzloe and O’Neal in separate lawsuits.

The grass-roots Tea Party activists, along with state Republicans, have homed in on a number of connections between Grayson and Guetzloe that have become fodder in the local media, especially in reports on the CBS affiliate, WKMG-TV.

Guetzloe serves on two business advisory boards set up by Grayson. A son of Guetzloe worked as an intern in Grayson’s congressional office last year. Federal Election Commission filings show that Grayson has paid nearly $50,000 to a polling firm that was incorporated in late 2008 by an on-and-off employee of Guetzloe, Victoria Torres, who is now herself running as a state candidate on the "Tea Party" ballot line that Guetzloe helped create.

Grayson also advertised on Guetzloe’s local radio program before it was canceled this year, with proceeds going directly to Guetzloe’s company, including, at least in June, a modest commission, station records show.

Guetzloe played down his connections to Grayson, saying that he is one of scores of people on Grayson’s advisory panels and that his son secured his internship at Grayson’s office through his school.

"This has nothing to do with the Democratic Party; it has nothing to do with Alan Grayson," said Guetzloe in an interview at a Cracker Barrel restaurant.

In an interview outside his house, Grayson dismissed as "conspiracy theories" any suggestion that he had any contact with Guetzloe regarding the "Tea Party" ballot line.

"The Republican Party of Florida wants people to think that there’s something here," he said. "The old saying where there’s smoke there’s fire? Here there’s not even any smoke."

Late last month, in a legal battle between Guetzloe and grass-roots Tea Party activists who accuse him of hijacking their movement, Wade C. Vose, a local election lawyer representing them, issued a subpoena for Grayson to sit for a deposition. Grayson was also ordered to share all written or electronic communications he had had with Guetzloe, members of the registered "Tea Party" and others. That deposition was to take place Thursday.

Last week, however, Guetzloe dropped his defamation suit, filed in May, citing procedural wrangling with Vose — scuttling the order for Grayson to answer questions.