Federal officials investigating Mayor Vincent C. Gray’s 2010 campaign have focused recently on allegations that campaign staff members encouraged some supporters to donate by promising that their contributions would not be reported, several people familiar with the investigation said.

The promises were allegedly made to city employees and contractors who feared that then-Mayor Adrian M. Fenty’s administration would retaliate if their contributions to Gray’s campaign became known, said three people who spoke on the condition of anonymity to comment candidly about the investigation. At the time, Gray was challenging Fenty for the Democratic nomination for mayor.

FBI investigators are trying to determine whether donations were concealed in violation of campaign laws, according to several people familiar with the investigation. City law requires the disclosure of all campaign donations to the Office of Campaign Finance.

Separately, The Washington Post has discovered discrepancies between an internal campaign list of nearly 2,750 contributions and reports that the Gray campaign filed with the campaign finance agency. The names of dozens of those donors do not appear in documents filed with the agency, according to a Post analysis.

The federal investigation — entering its 21st month — continues to hang over Gray, who made promises of greater integrity and transparency during his campaign for mayor. The mayor has said repeatedly that he will not comment on the investigation because it is ongoing. But in a brief interview Tuesday, he said he was surprised by the most recent allegations. “I’m astounded,” said Gray, who has denied any wrongdoing. “I’m incredulous.”

A growing list of Gray investigations
More people interviewed

In recent weeks, investigators have interviewed Barbara Lang, president and chief executive of the D.C. Chamber of Commerce and a new board member of the Metropolitan Washington Airports Authority, according to two other people, who have knowledge of the probe and who requested anonymity to speak freely.

Investigators asked Lang whether the Gray campaign chairman, Lorraine Green, told her that contributions from hesitant donors could be accepted without being reported, the two people said. Investigators also talked to Lang’s husband, Gerald, who was a member of the Gray campaign finance committee.

A. Scott Bolden, an attorney for the Langs, said they were interviewed by the FBI, but he declined to give details of the meetings.

“I can confirm that my clients, like several others, have been contacted by the FBI in connection with the Gray investigation and that both of them were open, honest and forthright in their interviews and are mere witnesses — not targets or subjects of the investigation. I remain confident that their status will not change,” Bolden said in a statement. “Furthermore, my understanding of those interviews is that neither of them knew very much and have little, if any, information to provide the U.S. Attorney concerning the Gray campaign’s fundraising operation.”

Thomas C. Green, an attorney for Lorraine Green, no relation, declined to comment.

If unreported donations were solicited, it is unclear which campaign staffers participated, how many donors were contacted or how much money was raised. But those alleged contributions would be separate from the funding of what federal prosecutors have called a “shadow campaign” — an illicit $653,800 get-out-the-vote covert operation on behalf of Gray.

“People on the [campaign] finance committee would say so-and-so can’t give,” said a committee member who demanded anonymity to speak freely. “Other people were apprehensive about giving to Gray. . . . That would happen. Frankly, people were worried about retribution. That happens in any campaign.”

The committee member remembered discussions about lagging campaign fundraising but was not aware of an effort to solicit secret donations.

“They have been asking questions,” said another person familiar with the investigation’s new focus, adding that the queries have been about alleged unreported donations.

Lists of contributors

According to the internal campaign document obtained by The Post, 2,744 contributions were made to Gray’s campaign from late March 2010 through mid-August of that year. But the document does not show donation amounts. The Post found about 60 contributors whose names and addresses did not appear in Office of Campaign Finance documents.

They do not appear to be the contractors and city employees allegedly solicited by those campaign staff members whose activities sources say are the subject of the federal probe. Instead, they gave much smaller amounts, between $25 and $50, according to interviews with a half-dozen donors.

If unreported donations were made to Gray’s official campaign, donations similar to those made to the “shadow campaign,” they would violate city campaign finance law.

Public relations consultant Jeanne Clarke Harris, as part of a guilty plea in July, admitted her role in the shadow campaign, which federal prosecutors say was a well-funded effort to elect Gray that was not disclosed to campaign finance authorities. She said in court that businessman Jeffrey E. Thompson provided the money but did not want Fenty to know that he was supporting Gray. Thompson, who was then the city’s largest contractor, has not been charged.

According to court filings, the funds paid for about 10,000 yard signs, 6,500 T-shirts and 200 umbrellas, in addition to banners, lapel stickers, posters, consultants, canvassers, drivers and computers. Many items were identical to Gray’s official campaign materials, and many were bought from the same vendors, prosecutors have said.

In a related development, Thomas W. Gore, the assistant treasurer of Gray’s campaign, is scheduled to return to U.S. District Court on Wednesday after pleading guilty in May to three D.C. election law misdemeanors and a federal charge of obstruction of justice.

Gore has admitted to taking part in covert payments to Sulaimon Brown, a mayoral candidate who has said he was paid by the Gray campaign to disparage Fenty during the Democratic primary race. Gore, who agreed to cooperate with the investigation, faces 12 to 18 months in prison. Howard L. Brooks, a campaign aide who made payments to Brown, was sentenced to two years of probation on a felony charge of making a false statement.

One of the donors listed on the internal document obtained by The Post is retired beautician Rosie Lee Moses, 90, of Northwest Washington. But it is unclear what happened to her donation because, like many others, it does not appear on the official campaign finance record.

Moses said she mailed a $50 check to the campaign but now regrets it, fearing that her contribution did not reach the official campaign.

Asked whether she still supports Gray, Moses said, “No comment.”

As for her donation, “I’d be glad to get it back,” she said.

Jennifer Jenkins contributed to this report.