WASHINGTON — The Army is investigating its top sex-crimes prosecutor on allegations that he groped a female lawyer at a sexual-assault conference in 2011, Army officials disclosed Thursday.

Lt. Col. Joseph Morse, who supervises 23 other special-victims prosecutors for the Army, was recently placed under criminal investigation after the female lawyer reported the alleged 2011 incident, officials said. News of the case was first reported Thursday by Stars and Stripes, a newspaper that covers military affairs.

Morse has not been charged in the case, but the revelation is the latest blow to the Pentagon as it struggles to cope with what some leaders have acknowledged is a epidemic of sexual assaults in the ranks.

News of the investigation surfaced just hours before the Senate was scheduled to vote on bills that would impose major changes in military law to strengthen the investigation and prosecution of sex crimes.

The investigation of Morse could give ammunition to both sides. Victim advocacy groups and some lawmakers have said that the armed forces are too lax on sex crimes and that major legal reforms are necessary. But other lawmakers, and many commanders, say that giving more power to prosecutors won’t fix the problem.