WASHINGTON Congressional investigators have questioned House Majority Leader Steny Hoyer and aides to Speaker Nancy Pelosi as part of a probe into whether top Democrats covered up information that ex-Rep. Eric Massa sexually harassed male employees.

The FBI has also been drawn into the Massa case, apparently by reports last weekend about a $40,000 check from the former congressman's campaign fund to his former chief of staff, who has filed a sexual harassment complaint against Massa, said an attorney involved in the case.

The House Ethics Committee formally opened its investigation on Wednesday. A four-member panel of the evenly divided committee questioned Hoyer, the Maryland Democrat's office said. In February, Hoyer's staff learned of the allegations against Massa, and Hoyer demanded that Massa's aides take them to the ethics panel.

Five months earlier, Massa's chief of staff met with an aide to Pelosi to complain about the conduct of Massa, D-N.Y. Pelosi aides have insisted that those discussions did not include the sexual harassment allegations.

"The speaker has made herself available to meet with ethics committee at their earliest convenience," said Nadeam Elshami, a spokesman for Pelosi. Elshami said members of Pelosi's staff have already met with and fully cooperated with the committee.

Massa, 50, resigned from the House last month after the sexual harassment allegations surfaced. The ethics committee cannot investigate former members, but it can look into what others did - or did not do - with knowledge of Massa's conduct.

Debra Katz, a lawyer for a former Massa staffer who last month filed a sexual harassment complaint against Massa, said Wednesday she had been contacted by the FBI's public corruption unit.

Katz said the FBI asked that her client, whom she refused to identify, preserve all documents that he had in his possession involving the ex-congressman. She said the FBI is not investigating the sexual harassment complaint.

"I presume their focus is on issues raised over the weekend," Katz said.

Massa's campaign cut a check for $40,000 to his chief of staff, Joe Racalto, who also has filed a sexual harassment complaint against Massa.

The unidentified staffer alleged in the March 23 complaint that Massa regularly groped him, propositioned him and made lewd remarks to him and other staffers, Katz said.

Aggressive sexual overtures by Massa were routine in the freshman lawmaker's congressional office, Katz said. They began in early 2009 shortly after Massa took office and escalated over time, particularly after Massa had been drinking, she said.

To emphasize the importance of the case, the ethics panel investigation is being headed by committee Chairman Zoe Lofgren, D-Calif., and ranking Republican Jo Bonner of Alabama.

The case has political importance this year. Republicans have tried to make the ethical conduct of Democrats a campaign issue, turning the tables on an issue that Democrats used successfully against Republicans to win control of the House in 2006.

Rep. Charles Rangel, D-N.Y., stepped aside as chairman of the House Ways and Means Committee last month after the ethics panel admonished him for allowing corporate money to pay for two trips to Caribbean conferences.

Pelosi's office has acknowledged that Racalto met with Pelosi's staff member and discussed a news story in Massa's hometown paper. The article described Massa's living in a residence with aides on his staff. Racalto told the speaker's office that he had told Massa, who is married, that he should move out. Pelosi's office said Racalto also discussed Massa's use of strong language and the way he ran his office.

The ethics investigation will look into whether House members or employees:

-Had personal knowledge, or were made aware, of Massa's conduct.

-Failed to properly report or fully disclose allegations of misconduct.

-Had a duty to pursue or call attention to the allegations.

The committee said it will also investigate whether money or other payments may have been misappropriated, or fraudulently or improperly distributed.

Racalto's lawyer, Camilla McKinney, said last week that the $40,000 check was a "deferred payment" for Racalto's work this year and last year on Massa's 2010 re-election campaign and for his work on Massa's transition after the 2008 election.

Massa, however, said the next day in a statement that he did not authorize the $40,000 check from his campaign account for Racalto. Massa also said that someone forged a $40,000 salary increase for Racalto on his congressional payroll.

McKinney disputed Massa's account, saying both transactions were done at Massa's direction. She questioned the timing of the allegations in light of Racalto's sexual harassment complaint against Massa, which was filed March 23, but didn't come to light until last week.

Associated Press writer Andrew Miga contributed to this report.