Barack Obama, the US president, has called for a repeal of the policy that was introduced in 1993 as a compromise between then president Bill Clinton's desire to lift the ban, and concerns from Congress and the military that lifting it would be disruptive.
Appearing before the same panel, Robert Gates, the defence secretary, announced a year-long policy review.
If the ban is revoked, it would mark the biggest shake-up to military personnel policies since President Harry Truman's 1948 executive order integrating the services.
"You don't have to be straight to shoot straight"
Mark Udall, Democratic senator
But some high-ranking military officers are reluctant to embrace the change.
John McCain, a Republican senator, said he was "deeply disappointed" at the Pentagon's decision to the survey.
"Has this policy been ideal? No, it has not,'' McCain, a former Navy officer, said.
"But it has been effective."
Several other Republicans sided with McCain, warning Mullen and Gates not to pursue a change at a time when the US was fighting two wars in Iraq and Afghanistan, and facing a continuing threat of terrorism.
Democrats said they would back a change in policy.
Mark Udall, a Democratic senator, said his Colorado constituents pride themselves
on allowing others to live and let live.
"You don't have to be straight to shoot straight,'' Udall said, quoting libertarian Barry Goldwater.
'Voting against soldiers'
Gay rights activists have complained that Obama has been slow in fulfilling a campaign promise to eliminate the policy.
Dan Choi, an Iraq war veteran and a gay rights activist who publicly challenged the "don't ask, don't tell" policy, told Al Jazeera he is facing discharge from the army after announcing that he was gay.
"I'm not satisfied with what happened today," Choi said.
"Soldiers who are gay have to lie about who they are. Unless we repeal the law today and the president uses his authority to stop firing people for their honesty, we've lost all moral high ground in the world.
"When they [the military] presume that our soldiers will lose all control once you allow honesty to swell the ranks that really is voting against our soldiers.
"It's saying our soldiers aren't dependable or professional or disciplined enough to handle the truth."
Under the 1993 law, engaging in homosexual conduct - even if the person concerned does not tell anyone - can be enough to qualify a person for dismissal.
Recent figures from the Pentagon show that 428 service members were dismissed for being openly gay in 2009, down from 619 dismissed in 2008.
The number is by far the lowest since 1997, when 997 service members were dismissed.
Overall, more than 10,900 troops have been dismissed under the policy.