Washington (CNN) -- Allowing openly gay or lesbian troops serve in the military would have little lasting impact on the U.S. armed forces, according to a long-awaited Pentagon review of the controversial "don't ask, don't tell" policy.
Repealing the policy would have "some limited and isolated disruption to unit cohesion and retention," the year-long study found, but the effects would not be long-lasting or widespread.
"The general lesson we take from ... transformational experiences in history is that in matters of personnel change within the military, predictions and surveys tend to overestimate negative consequences, and underestimate the U.S. military's ability to adapt and incorporate within it ranks the diversity that is reflective of American society at large," the report concluded.
President Barack Obama used the release of the report to urge the lame-duck Senate to follow the lead of the House of Representatives and pass a repeal of the Clinton-era law before the end of the year.
This report confirms that "by every measure -- from unit cohesion to recruitment and retention to family readiness -- we can transition to a new policy in a responsible manner that ensures our military strength and national security," Obama said in a written statement.
"Our troops and their families deserve the certainty that can only come when an act of Congress ends this discriminatory policy once and for all."
Secretary of Defense Robert Gates also urged the Senate to act quickly, warning that the military doesn't want change imposed by "judicial fiat." Speaking at the Pentagon, he alluded to a recent string of court opinions calling the legal viability of the current policy into doubt.
A repeal forced by the courts would be the most damaging scenario imaginable, he said. Those who choose not to act legislatively "are rolling the dice" that "change won't be forced by the courts."
Both Gates and Joint Chiefs of Staff Chairman Adm. Mike Mullen back a repeal of the law.
There is, however, strong minority opposition to a change, particularly in the Marines and some combat arms specialist units, according to the chairs of the study, Defense Department General Counsel Jeh C. Johnson and Army Gen. Carter F. Ham.
As many as 40 to 60 percent of troops in those units were against changing the 17-year-old policy that lets gay and lesbian troops serve as long as their sexual orientation is secret.
Overall opposition throughout the military was about 30 percent -- roughly the same as it is in America as a whole, according to recent findings from CNN/Opinion Research Corp. and the Pew Forum.
Johnson told members of Congress on Tuesday that he thought "don't ask, don't tell" could be repealed even while the United States is at war, sources said.
More than nine out of 10 troops said their unit's ability to work with someone they thought was gay or lesbian was very good, good, or neither good nor bad.
The authors of the report say gay and lesbian troops would continue to be discreet about their personal lives, even with a repeal, based on observations of workplaces in civilian society.
"I think a lot of people think there is going to be this big 'outing' and people flaunting their gayness, but they forget that we're in the military," one service member said. "That stuff isn't supposed to be done during duty hours regardless if you're gay or straight."
Another service member said, "I don't feel that this is something I should have to disclose. Straight people don't have to disclose their orientation. I will just just be me. I will bring my family to family events. I will put family pictures on my desk. I am not going to go up to people and say, 'Hi, there, I'm gay.' "
One Special Forces operative -- a part of the military with overall higher resistance to the change -- said, "We have a gay guy [in the unit]. He's big, he's mean, and he kills lots of bad guys. No one cared that he was gay."
The authors said they did hear a large number of religious and morally based objections to homosexuality.
"A large number of military chaplains believe that homosexuality is a sin and an abomination and that they are required by God to condemn it as such," the report notes.
But the report also points out that different moral values and religious convictions already exist inside the U.S. military and that while chaplains and others won't be required to change their personal views and beliefs, they must respect and serve others.
The report goes into detail over concerns that allowing gays to serve openly would create invasions of privacy and discomfort over sharing bathrooms or living facilities.
"We disagree and recommend against separate facilities," it concludes. "The creation of a third or possibly fourth category of bathroom facilities and living quarters, whether at bases or forward deployed areas, would be a logistical nightmare, expensive and impossible to administer."
"Separate facilities would in our view stigmatize gay and lesbian Service members in a manner reminiscent of 'separate but equal' facilities for blacks prior to the 1960's," the report states.
The report suggests not making gays and lesbians in the military a special class of military personnel, for diversity programs or complaint resolution.
"In a new environment in which gay and lesbian Service members can be open about their sexual orientation, we believe they will be accepted more readily if the military community understands that they are simply being permitted equal footing with everyone else," it says.
The report also says that men and women removed from the military under the current "don't ask" rules should be allowed to return, without the reason for their dismissal being considered as part of their application.
On the issue of benefits, the authors urge more study, including a full review of any policy change in a year. Even with a repeal of "don't ask, don't tell," not all benefits would be available to gay service members and their partners because of the Defense of Marriage Act.
The authors of the report point to military housing as one area of likely difficulty.
"We do not recommend at this time that military family housing be included in the benefits eligible for this member-designated approach. ... Military housing is a limited resource and complicated to administer and a system of member designation would create occasions for abuse and confusion," the report says.
The recommendations are based on surveys, focus groups and face-to-face meetings at bases around the world and even a carefully controlled effort to communicate anonymously with homosexuals serving in the military.
The Pentagon sent surveys to 400,000 troops and got about 115,000 responses. It sent separate questionnaires to 150,000 military spouses and got 44,000 back.
The Defense Department also set up a website for service members who wanted to comment. That effort elicited 72,000 responses.
And the Pentagon held meetings at 51 U.S. military bases around the world where 24,000 more troops discussed the issue.
Officials preparing the report also went to the service academies to hear from staff, faculty and students.
Social conservative activists, however, were quick to attack the report.
"The surveys did not ask whether respondents support repeal of the current law," said Tony Perkins, head of the Family Research Council. "If most service members say that under a different policy, they would continue to attempt to do their job in a professional manner, that is only what we would expect. This does not mean that a new policy would not undermine the overall effectiveness of the force.
"If even a small percentage of our armed forces would choose not to re-enlist, or part of the public would choose not to serve in the first place, the impact on the military would be catastrophic," he argued.
Sen. Lindsey Graham, R-South Carolina, echoed Perkins' complaint, saying the authors of the survey "didn't ask the right questions" because it was "all about how you implement the repeal, not should it be repealed."
Graham also criticized the House's decision to pass a repeal of "don't ask, don't tell" before the study was concluded.
"We spoke on the middle of a survey, which I think tainted the whole process," he said.
In October, Gates wrote in a letter to Sen. John McCain, R-Arizona, that it was not part of the charter of the Pentagon's so-called working group to poll the troops on whether the "don't ask, don't tell" policy should be repealed.
"I do not believe that military policy decisions should -- on this or any other subject -- be subject to referendum of service members," Gates wrote.
His letter to McCain has not been released, but a Pentagon source confirmed the accuracy of the quote.
On Thursday, the Senate Armed Services Committee will hear directly from Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff. On Friday, it will hear from the top brass of the Army, Navy, Air Force and Marines.
Outside the military, Americans are overwhelmingly in favor of repealing the current law.
A Pew survey released Monday indicated that a majority of Americans say they favor allowing gays and lesbians to serve openly in the armed forces.
According to the poll, 58 percent of the public approves of allowing homosexuals to serve openly, with 27 percent saying they are opposed.
A CNN/Opinion Research Corp. poll conducted earlier in November indicated that more than seven in 10 Americans said that people who are openly gay or lesbian should be allowed to serve in the military, with 23 percent opposed.
Despite public opinion on the side of repeal supporters, 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 U.S. 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.
Gen. George Casey, the Army chief of staff, has said he is on board with Gates in considering the effect of the repeal. But committee members may remind him of something he told them earlier.
"I do have serious concerns about the impact of the repeal of the law on a force that's fully engaged in two wars and has been at war for eight and a half years," Casey said this year.
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 part of the Defense Authorization Bill or whether to strip it off for a separate vote.
But the calendar could be the biggest factor weighing on whether the law is repealed or upheld. With just weeks left for this Congress with its significant Democratic majority, the leadership will need to decide whether it has the time, amid other priorities it wants considered, to mire the Senate in debate about "don't ask, don't tell."
CNN's Alan Silverleib, Ed Hornick, Gabriella Schwarz and Paul Steinhauser contributed to this report.