US defense leaders pushed back Thursday against Republican senators opposed to allowing gays to serve openly in the military, saying troops are ready for the change.

The US military’s top officer, Admiral Mike Mullen, and Defense Secretary Robert Gates pointed to a new Pentagon study as proof the armed forces would not suffer a traumatic upheaval if the gay ban was lifted, as some conservative lawmakers have warned.

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“I believe that in the long run, repeal of this law makes us a stronger military and improves readiness. It will make us more representative of the country we serve,” Mullen told the Senate Armed Services Committee.

Mullen and Gates also rejected Republican senators’ argument that the change should be postponed in wartime.

“If not now, when?” asked Gates, saying he did not expect global threats to recede for the United States in the years to come.

Mullen said being at war was an argument for moving ahead on the issue rather than putting off action, as years of combat since 2001 have made the military more flexible and more accepting of change.

“War does not stifle change; it demands it. It does not make change harder; it facilitates it,” the admiral said.

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The Pentagon report released Tuesday found a “solid majority” of troops did not believe ending the ban would have a damaging effect, though members of mostly-male combat units had more concerns.

Mullen said the Pentagon study confirmed his belief that the military could carry out the change without disruption and military attitudes have evolved since the “Don’t Ask, Don’t Tell” law was adopted in 1993.

“I believe our troops and their families are ready for this. Most of them already believe they serve or have served alongside gays and lesbians,” he said.

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The law, opposed by a majority of Americans according to numerous polls, requires gay and lesbian troops to keep their sexual orientation quiet or face discharge from the military.

Republican senators said ending the ban posed risks to a military already strained by two wars in Afghanistan and Iraq, pointing to results of the study that showed 40 to 60 percent of troops in combat units feared the change would have a negative effect.

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“I am concerned about the impact of a rush to repeal when even this survey has found that such a significant number of our service members feel that it would negatively impact military effectiveness,” Senator John McCain said.

Obama and his allies in Congress are pressing for action on the issue during a year-end “lame duck” session, before the Democrats’ majority dwindles in the Senate and Republicans take control of the House of Representatives in January.

The legislation needs 60 votes in the Senate to overcome any parliamentary delaying tactics, and Democrats are counting on gaining a handful of Republican votes needed to proceed.

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At the hearing that split along party lines, McCain and other Republicans criticized the Pentagon study for not explicitly asking troops whether they supported repealing the ban.

But Gates said the study was designed to look at the possible impact of repeal and that the US government did not poll the military to decide policy.

“Are you going to ask them if they want 15-month tours?” he asked.

Mullen, chairman of the Joint Chiefs of Staff, said the law contradicted the military’s principles of honor and integrity by forcing gay service members to lie about who they are.

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“Our people sacrifice a lot for their country, including their lives. None of them should have to sacrifice their integrity as well,” he said.

“I would not recommend repeal of this law if I did not believe in my soul that it was the right thing to do for our military, for our nation and for our collective honor.”

Unlike Mullen, the head of the Marine Corps and chiefs of other armed services have argued against ending the ban or voiced concern about making the change in wartime.

Republican supporters of the ban have seized on the views of the service chiefs, who were due to testify before the same committee on Friday.