However, eliminating the current "don't ask, don't tell" policy will cause "some disruption in the force," Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee.
"I cannot escape being troubled by the fact that we have in place a policy which forces young men and women to lie about who they are in order to defend their fellow citizens," Mullen said.
Defense Secretary Robert Gates told the panel that he "fully supports" President Obama's decision to work with Congress to end the policy.
Several committee Republicans, led by the ranking member, Sen. John McCain of Arizona, said they were disappointed with Obama's decision and supported retaining the "don't ask, don't tell" policy. Committee Chairman Carl Levin, D-Mich., praised Mullen's personal endorsement for lifting the ban as a "profile in leadership."
McCain said, "At this moment of immense hardship for our armed services, we should not be seeking to overturn the 'don't ask, don't tell' policy."
Gates told senators the military would need nearly a year to study how it would allow gay men and lesbians to serve openly.
Pentagon general counsel Jeh Johnson and Gen. Carter Ham, commander of Army forces in Europe, will lead the group studying troops' feelings about lifting the ban on gays serving openly in the military, Gates said.
Ham, an Iraq veteran, is rare among high-ranking military officers in talking about his experiences with combat stress. In November 2008, he told USA TODAY how he struggled to cope with a 2004 attack in Mosul that killed 22 people, including 14 U.S. troops.
"That there will be some disruption in the force I cannot deny," Mullen said of lifting the ban. "That there will be legal, social and perhaps even infrastructure changes to be made certainly seem plausible."
He also cautioned that military commanders worry about the current war stress on troops and their families. "We need to move forward (with changing policy on sexual orientation) in a manner that does not add to that stress."
Mullen is the first sitting chairman of the Joint Chiefs of Staff to advocate repeal of "don't ask, don't tell," according to a statement from his office.
The policy bans openly gay people from serving in the military but also says that military officers should not ask members of the military about their sexual orientation if they are not engaging in prohibited behavior. The policy was created in 1993 after President Clinton sought to allow openly gay people to serve. Overall, records show, more than 10,900 servicemembers have been dismissed under the policy.
Mullen said allowing lesbians and gay men to serve openly is "an issue of integrity — theirs as individuals and ours as an institution. ... I also believe the great young men and women of our military can and would accommodate such a change."