* Republicans question Pentagon study, fear fallout
* Obama wants to end ban this year, faces uphill battle
* Military divided, top officer strongly backs repeal
By Phil Stewart
WASHINGTON, Dec 3 (Reuters) - U.S. military chiefs told the Senate on Friday they opposed ending the armed forces' ban on gays anytime soon, urging caution over President Barack Obama's effort to repeal the "Don't Ask, Don't Tell" policy.
"This is a bad time, senator," Marine Corps Commandant James Amos told a hearing of the Senate Armed Services Committee.
"Based on what I know about the tough fight on the ground in Afghanistan ... my recommendation is that we should not implement repeal at this time."
The dissent, most strongly articulated by the Marines and to lesser degrees the Army and Air Force, was widely expected and echoed past warnings about adding strain on a force already stretched by wars in Afghanistan and Iraq.
The dim view was not shared by all top U.S. officials testifying. The chiefs of the Navy, Coast Guard and the vice chairman of the Joint Chiefs of Staff backed repeal.
Admiral Mike Mullen, who is the top U.S. military officer as chairman of the Joint Chiefs of Staff, on Thursday voiced his strong support for repeal, as did U.S. Defense Secretary Robert Gates.
But the latest dissent could bolster Republican efforts to block Senate action on ending the 17-year-old policy, which allows gays and lesbians to serve as long as their sexual orientation is not revealed.
Senator John McCain, a top Republican and decorated veteran of the Vietnam War who lost to Obama in the 2008 presidential election, said he opposed any vote on repeal this year.
"It's very obvious to me that there is a lot more scrutiny and work to be involved before passing this legislation," he said. "That's why we see such a diversity of views here among the service chiefs."
Obama campaigned for the presidency in 2008 on a pledge to fully repeal the law barring gays and lesbians from serving openly in the military.
The effort, however, faces a promised Republican procedural roadblock in the 100-member Senate. It is unclear if Democrats can muster the needed 60 votes to pass it.
A Pentagon study released on Tuesday predicted little impact if the ban were repealed but acknowledged a "significant minority" of about 30 percent overall expressed negative views or concerns about repeal. That figure was higher in the Marine Corps and generally rose among combat units.
Gates and Mullen said training could mitigate risks from repeal. They said the measure before the Senate would not allow the repeal to be implemented until Obama, Gates and Mullen certify the military is ready.
They also rejected arguments that the military was too strained by the wars in Iraq and Afghanistan to integrate openly serving homosexuals.
"War does not stifle change. It demands it," Mullen told the same committee on Thursday.
But Army Chief of Staff General George Casey disagreed on Friday, saying: "The fact that we're at war complicates repeal."
Asked about Mullen's comments, Casey acknowledged that in some cases the close bonds formed among troops at war could "facilitate" integration of openly gay and lesbian troops.
"But frankly, I think that's a bit of a stretch," he said. (Editing by Bill Trott)
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