MELBOURNE — The US military's top officer on Monday said he was "surprised" at public remarks by the head of the Marine Corps who questioned the repeal of a ban on gays serving openly in the armed forces.

Admiral Mike Mullen, chairman of the US Joint Chiefs of Staff, said service chiefs were expected to offer their best military advice on the issue "privately," suggesting the commandant of the Marine Corps had stepped out of line by speaking publicly.

"Actually I was surprised. I was surprised what he said, surprised he said it publicly," Mullen told reporters at a briefing in Melbourne.

General James Amos, the new head of the US Marine Corps, told The Los Angeles Times in an interview published Sunday that he was concerned about the effect of ending the ban -- as proposed by President Barack Obama -- at a time when US troops are in combat.

Amos, who assumed command of the elite force two week ago from General James Conway, said he was worried about the impact on unit cohesion and readiness if "Don't Ask, Don't Tell" ended.

The 1993 law was a compromise that forbids gays from serving openly in the military, but also is supposed to bar the military from questioning troops about their sexual orientation.

With a Pentagon study of the issue due by December 1, Mullen said the heads of each military service had agreed to "to come together" and "look at the data and make our recommendations privately" about the impact of lifting the ban.