WASHINGTON - A senior law enforcement agent accused of taking bribes in a Navy corruption scandal has agreed to plead guilty and cooperate with investigators, a major break in a case that has ensnared half a dozen Navy officers and threatens to tar more.

John B. Beliveau II, a supervisory special agent with the Naval Criminal Investigative Service, is scheduled to enter a guilty plea Tuesday in U.S. federal court in San Diego, according to court records and his attorney. Beliveau was arrested in September and charged with helping a Singapore-based Navy contractor, Glenn Defense Marine Asia, dodge multiple criminal investigations by leaking inside information about NCIS probes in exchange for prostitutes, cash, and other favors.

"He will be pleading guilty and admitting his conduct," said his attorney, Gretchen Von Helms of San Diego. She declined to comment further, saying that terms of his plea deal would remain confidential until he appears in court next week.

Kelly Thornton, a spokeswoman for the U.S. Attorney's Office in San Diego, confirmed that Beliveau is scheduled to appear in court Tuesday for a change of plea hearing but also declined to comment.

Two people involved in the case, speaking on condition of anonymity because details have not been presented in court yet, said Beliveau had agreed to share information with federal prosecutors about his extensive relationship with Leonard Glenn Francis, the president of Glenn Defense Marine and a codefendant in the case, as well as others involved in the probe.

Known in Navy circles as "Fat Leonard" for his imposing physical presence, Francis is a Malaysian citizen and a well-known figure to scores of Navy officers whose ships depended on his firm for logistical support during Asian port visits. He has pleaded not guilty. One of his attorneys, David S. Black of Washington, did not return phone calls for this article.

Beliveau's guilty plea would mark a big advance for investigators, who are trying to determine the scope of the alleged corruption involved in the awarding and administering of lucrative Navy contracts for port services in Asia.

In addition to Beliveau, two Navy commanders have been arrested and charged with taking bribes. Two captains have been suspended or reassigned by the Navy. And two admirals who work in Navy intelligence have had their access to classified materials suspended while investigators scrutinize their possible involvement.

According to charging documents filed by prosecutors, Beliveau helped to thwart multiple fraud investigations into Glenn Defense Marine by surreptitiously copying sensitive records from the case files of other NCIS agents and feeding the details to Francis.

From 2005 through 2008, Beliveau served as a protective service agent for the commander of the Navy's Seventh Fleet, based in Japan. From 2008 until 2012, he was stationed in Singapore, where he was responsible for meeting Navy ships and arranging protection for their visits.

It's unclear when Beliveau first met Francis, but the charging documents state that the pair were in "regular contact" over the last five years.

In 2010, the NCIS opened two separate fraud investigations into suspicions that Glenn Defense Marine had overcharged the Navy for port visits in Thailand and Japan.

In both cases, according to prosecutors, Beliveau sent e-mails to Francis, tipping him off to developments in the probes and advising him on how to respond to agents' queries. The investigations soon stalled and Francis bragged in an e-mail to an associate that "both are hard to prove and charge. I have inside Intel from NCIS and read all the reports," charging documents show.

In early 2012, NCIS opened another investigation into Glenn Defense Marine on suspicion that it was overbilling the Navy with fake subcontractor bids. Around the same time, Beliveau took a new NCIS job as a supervisory agent in Quantico, Va.

According to prosecutors, Francis once again turned to Beliveau for help. This time, however, Beliveau balked.

"I will always be your friend, but you will get nothing else ... until I get what you promise," Beliveau wrote in an e-mail to Francis in late April 2012. "You give whores more money than me ;) ... Don't get too busy that you forget your friends ... Let me know ... I can be your best friend or worst enemy."