WASHINGTON — Legislation to curb sexual assaults in the military by stripping senior commanders of their authority to prosecute rapes and other serious offenses is headed for a highly anticipated vote in the Senate.

The bill, which was expected to come up for a vote this afternoon, is firmly opposed by the Pentagon’s leadership, which argues officers should have more responsibility, not less, for the conduct of the troops they lead.

A solid majority of the Senate backs the bill, sponsored by Sen. Kirsten Gillibrand, D-N.Y., illustrating the deep frustration among Republicans and Democrats over the military’s failure to stem the epidemic of sexual assaults in the ranks. Gillibrand, however, will likely need 60 votes to prevent a filibuster that would block the bill’s passage.

The Pentagon came under pressure last month to disclose more information about how sexual assault cases are adjudicated following an Associated Press investigation that found a pattern of inconsistent judgments and light penalties for sexual assaults at U.S. bases in Japan.

The AP’s investigation, which was based on hundreds of internal military documents, found that what appeared to be strong cases were often reduced to lesser charges.