The service chiefs of the Army and Marines have given Arizona Senator John McCain fresh political ammunition in his fight to keep “Don't Ask, Don't Tell.”

McCain and other senators who oppose repeal of the law that bans gay and bisexual troops from serving openly will undoubtedly use Friday's testimony before the Senate Armed Services Committee to push back against Democratic leaders who have promised a vote this month on repeal of the 17-year-old law.

“If the law is changed, successfully implementing repeal and assimilating openly homosexual Marines into the tightly woven fabric of our combat units has strong potential for disruption at the small unit level, as it will no doubt divert leadership attention away from an almost singular focus of preparing units for combat,” James Amos, commandant of the Marine Corps, testified.

Army Chief of Staff General George Casey rated the risk of repeal to his force as moderate, arguing that lifting the policy at a time of war would “add another level of stress to an already stretched force.”

Both men pointed to a Pentagon report on repeal released Tuesday that found a high number of Marine and Army combat troops opposed to repeal.

Secretary of Defense Robert Gates, who has previously urged Congress to end the ban, dismissed the report's findings during Thursday's hearing, saying that combat soldiers have limited experience in the military.

“With time and adequate preparation, we can mitigate their concerns,” Gates said.

Overall, the report's survey of the troops found that 70 percent are okay with serving alongside openly gay service members. McCain has called the report flawed because it had not asked troops if the law should be repealed, a question Gates has previously rejected as inappropriate.

The chief of naval operations, Admiral Gary Roughead, and Air Force Chief of Staff General Norton Schwartz also noted the concerns of combat troops. Schwartz suggested deferring repeal until 2012. Roughead recommended repeal.

In his testimony, General James Cartwright, the vice-chairman of the Joint Chiefs of Staff, agreed with the chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, who testified in favor of repeal on Thursday.

“The character and appeal of the U.S. armed forces lies in the inclusivity, equality and opportunity in our organizational ethos,” he said. “Being more inclusive, in my view, will improve the institution as a whole.”