WASHINGTON - As promised, the Pentagon has begun examining how the ban on gays serving openly in the military could be eased and then repealed, but a complete repeal of the "don't ask, don't tell" policy is probably years away.

The two officials appointed to lead a yearlong internal assessment -- Gen. Carter Ham, commander of U.S. Army forces in Europe, and Pentagon General Counsel Jeh Johnson -- met for the first time on Feb. 9.

As that study gets under way, officials were expected by mid-March to suggest ways to relax enforcement of the law. Of particular interest is minimizing cases of "third party outings," where a service member is kicked out after being reported by others to be gay.

The protracted time line is about more than giving military leaders time to assess the impact on troops and put new rules in place. The multiyear process also is a strategic way of getting troops used to the idea before they have to accept change.

Reversing the military's policy on gays, which is based on a 1993 law and would require an act of Congress, would mark the biggest upheaval to the military's personnel policies since the 1948 executive order on racial integration.

The goal, according to senior defence and military officials, is to avoid the backlash that could result from imposing change too fast. While officials expect resistance from only a minority of service members and believe that it could be contained with discipline, officials fear isolated incidents of violence could erupt as a means of protest.

Defence Secretary Robert Gates suggested as much in recent congressional testimony, when he said he had learned from "stupid" management attempts to dictate change too quickly as a senior CIA official in the 1980s.

"Stupid was trying to impose a policy from the top without any regard for the views of the people who were going to be affected or the people who would have to effect the policy change," Gates said.

As part of the internal review, Gates said the military would survey service members and their families on any changes to policies.

"A guiding principle of our efforts will be to minimize disruption and polarization within the ranks, with a special attention paid to those serving on the front lines," Gates told a Senate committee this month.

President Barack Obama, who says the ban is unjust, is counting on a major cultural shift among American voters in the 17 years since it went into effect. Then, Democratic lawmakers joined the military in resisting a proposal by President Bill Clinton that would have let gays serve openly.

Clinton emerged from the debate politically bruised, with Republican critics casting the new president as a social liberal who was woefully out of touch with the military.

The 1993 law does not explicitly prohibit gays or lesbians from serving in the military but requires them to serve in silence. If they acknowledge their sexual orientation or engage in a homosexual act, they can be expelled. But if not asked, they need not disclose it.

Since then, Democratic lawmakers have been reluctant to take on the issue as well. Since taking control of Congress three years ago, following the 2006 elections, Democrats have focused their efforts instead on more popular military-related issues like ending the war in Iraq.

According to a Washington Post-ABC News poll, three-quarters of Americans say that they support openly gay people serving in the military. The 75 per cent figure is far above the 44 per cent of Americans who said so in May 1993.

Former Vice-President Dick Cheney, defence secretary in the first Bush administration, said Sunday he supports a review of the policy.

"When the chiefs come forward and say we think we can do it, it strikes me it's time to reconsider the policy," he said. "I'm reluctant to second-guess the military in this regard."

Cheney, who has an openly gay daughter, said he thinks society has moved on from staunch opposition to gays serving in the military.

"It's partly a generational question," he told ABC television's "This Week," adding that "things have changed significantly" since the policy took effect.

Obama's national security adviser, retired Marine Gen. James Jones, said on CNN's "State of the Union" that the policy "has to evolve with the social norms of what is acceptable and what is not."