Authorities are looking into whether O’Keefe protected alleged bookmakers operating on the Cape and gave favorable treatment to the grandson of one of them in an unrelated criminal case, said the sources, who insisted on anonymity because grand jury investigations are confidential.

The full scope of the grand jury investigation is unclear, and there is no indication it will result in criminal charges against O’Keefe or anyone else. A number of witnesses have testified before the panel in Worcester in recent months, including a state judge on the Cape.

O’Keefe, a 59-year-old two-term Republican district attorney, issued a statement late yesterday denying he has done anything wrong.

“Some information has apparently been leaked from a federal grand jury concerning illegal betting,’’ he said. “I do not now nor have I ever had any association with gaming. Any assertion of wrongdoing by me or my office is completely false.’’

He added that his record as a prosecutor and former Dennis police officer over 30 years is “one of integrity and speaks for itself.’’ He said there will be no interruption in the work of his office.

The name of a prominent former public official has also come up in the investigation: former lieutenant governor Thomas P. O’Neill III. Now a lobbyist on Beacon Hill and a friend of O’Keefe’s, O’Neill, the son of the late US House Speaker Thomas P. “Tip’’ O’Neill Jr., was heard on a wiretap allegedly placing bets, said the sources. O’Neill declined to comment yesterday.

The grand jury began subpoenaing evidence at least 15 months ago, according to a document in the Barnstable District Court case file of the grandson of the convicted bookmaker.

The original investigation was initiated by Attorney General Martha Coakley in fall 2008 and focused on the activities of several alleged members of a Cape Cod-based gambling ring that included Adam Hart, a convicted bookmaker and longtime owner of the Ocean House Restaurant in Dennisport, said the sources.

But the focus shifted to O’Keefe early last year after a relative of Hart’s made a comment on the wiretap that triggered concerns for investigators that the district attorney may have protected illegal gamblers in the past, said people knowledgeable of the investigation. US Attorney Carmen M. Ortiz’s office then took the lead role in the investigation being conducted by the FBI and State Police.

Two federal prosecutors — Brian T. Kelly, the head of Ortiz’s public corruption unit, and Fred Wyshak, who prosecuted contractors in Big Dig fraud cases — are leading the grand jury investigation.