(CNN) -- Now is not the time to repeal the military's "don't ask, don't tell" policy on gay men and lesbians serving openly in the U.S. armed forces, Sen. John McCain said at a hearing Thursday.
"At this time, we should be inherently cautious about making any changes that would affect our military, and what changes we do make should be the product of careful and deliberate consideration," the Arizona Republican said at the Senate Armed Services Committee hearing.
His position is not that the law should never be changed, he said, but that "it may be premature to make such a change at this time and in this manner."
In contrast, Defense Secretary Robert Gates urged that the repeal be signed into law as soon as possible, to avoid the issue being taken up again by the judiciary, where a repeal of the ban could be ordered immediately, rather than on the military's timetable. A judicial fiat would be "hazardous," he added.
"This can be done, and should be done," Gates said of the policy change.
McCain questioned the results of a report that found that most military personnel would not change their career plans if the policy was changed, saying that only a fraction of military personnel responded.
He also noted that the survey found opposition to the change is much higher in Army and Marine combat units than elsewhere in the military.
The chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, said he believes that even among those combat forces, a transition to a new law is possible.
"Should repeal occur, some soldiers and Marines may want separate shower facilities. Some may ask for different berthing. Some may even quit the service. We'll deal with that. But I believe, and history tells, that most of them will put aside personal proclivities for something larger than themselves and for each other," he said.
In a tense exchange between Gates and McCain, the defense secretary reiterated Mullen's point.
"Most of the Marines who are in combat are 18 to 24 [or] 25 years old. Most of the them have never served with women, either. So they have had a very focused, very limited experience in the military and it's been a tough one," Gates said. "But I think that with time and adequate preparation we can mitigate their concerns."
McCain responded, "Well, I couldn't disagree more. We send these young people into combat. We think they are mature enough to fight and die. I think they are mature enough to make a judgment on who they want to serve with and the impact on their battle effectiveness."
McCain was upset that the military survey did not ask explicitly whether troops were in favor or against repealing "don't ask, don't tell." The questions asked how military units would respond and adapt if it were repealed.
Gates and Mullen argued that asking troops for their opinions on the repeal would be akin to a referendum on the policy, something that Mullen called a "bad precedent."
The argument did not sway McCain. He said that any good leader should get opinions from his subordinates before making a decision.
"I'm almost incredulous to see that on an issue of this magnitude, we wouldn't at least solicit the views of the military about whether this law would be changed or not," he said.
Mullen responded that the survey that was done gave an adequate amount of opinion, even if the question was not directly asked.
"We've gotten in great parts their views as a result of this survey," Mullen said.
On Friday, the committee will hear from the top brass of the Army, Navy, Air Force and Marines.
While a Pew survey showed that 58 percent of the public support repealing the ban, the heads of the four military branches have either directly opposed or been unenthusiastic about the policy change, at least until the Pentagon report was finished and released.
Marine Commandant James Amos has said that he opposes the change while the United States is fighting in Afghanistan because of its potential negative effect on unit cohesion. He will be joined on the second day of hearings by another Marine, the vice chairman of the Joint Chiefs, Marine Corps Gen. James Cartwright.
Once the Armed Services Committee's hearings are over, the spotlight will turn to Senate Majority Leader Harry Reid, D-Nevada. He will decide how the issue will move forward: whether to keep it as part of the Defense Authorization Bill or strip it off for a separate vote.
With just weeks left for this Congress, the calendar could be the biggest factor weighing on whether the law is repealed or upheld.
The House has already passed the repeal.