WASHINGTON - It's time to repeal the military's "don't ask, don't tell" policy and allow gay troops to serve openly for the first time in history, the nation's top defence officials declared Tuesday, with the chairman of the Joint Chiefs of Staff proclaiming that service members should not be forced to "lie about who they are."

However, both Defence Secretary Robert Gates and Joint Chiefs Chairman Adm. Mike Mullen asked for a year to study the impact before Congress would lift the controversial policy.

In the meantime, Gates announced plans to loosen enforcement rules for the policy, which says, in essence, that gays may serve so long as they keep their sexuality private.

Reversing the Pentagon's 17-year-old policy toward gays "comes down to integrity," for the military as an institution as well as the service members themselves, Mullen told a Senate hearing. Unpersuaded, several Republican senators said they would oppose any congressional effort to repeal the policy.

Ten months before voters elect a new Congress, some Democratic leaders also were leery of trying to change the policy this year, when both sides concede Republicans are likely to pick up seats, especially after Republican Sen.-elect Scott Brown's surprise victory last month in Massachusetts.

Repealing don't-ask-don't-tell is not a winning campaign strategy for a party under siege especially in the South and Midwest.

"What do I want members to do in their districts? I want them to focus on jobs and fiscal responsibility," said House Democratic Majority Leader Steny Hoyer, classifying gays in the military in a category of "a lot of other issues" that will invariably come up.

"It's never a good year" for Democrats to bring up the controversial policy, said Senate Democratic Whip Dick Durbin. "You can expect that it's going to be a rough ride."

However, Senate Majority Leader Harry Reid said he didn't see why it should wait another year.

The Pentagon announced an 11-month review of how the ban could be lifted, as President Barack Obama has said he will work to do. But there is no deadline for ending the policy, which dates to President Bill Clinton's tenure and that gay rights advocates are pressing to overturn.

Obama has called for repeal but has done little in his first year in office to advance that goal. If he succeeds, it would mark the biggest shake-up to military personnel policies since President Harry S. Truman's 1948 executive order integrating the services.

Homosexuality has never been openly tolerated in the American military, and the 1993 policy was intended to be a compromise that let gay men and women serve so long as they stayed silent about their sexuality. Clinton had wanted to repeal the ban entirely, but the military and many in Congress argued that doing so would dangerously disrupt order.

Repealing the ban would take an act of Congress, something that does not appear close to happening.

Since 'don't ask, don't tell" was established, much has changed. Five states and the District of Columbia have adopted laws permitting marriage of gay couples, while nine other states have granted similar rights to gay domestic partners.

The public's attitude toward gays and lesbians also has undergone a significant shift. A Pew poll last year indicated that 59 per cent of Americans favour allowing gays and lesbians to serve openly in the military, up from 52 per cent in 1994.

On Tuesday, several Democratic senators praised Mullen and Gates for what they said was courageous stance, but a number of Republicans spoke strongly against the idea of a repeal.

Gates drew unusually pointed criticism from Republicans on the Senate Armed Services Committee for saying the review would examine how, not whether, to repeal the ban. Arizona Sen. John McCain, the top Republican on the panel, icily told Gates he was disappointed in his position and suggested the Pentagon was usurping Congress' job.

"Has this policy been ideal? No, it has not," McCain said. "But it has been effective."

Tuesday's session gave Obama high-level cover on a divisive social issue complicated by the strains on an all-volunteer military force fighting two wars.

Gates, who says he is a Republican, is the only member of former President George W. Bush's Cabinet whom Obama asked to stay on. He has gained a reputation for both candour and caution. Mullen's words were a forceful endorsement from a careful man, and his very appearance, starched uniform and four stars on view, made a statement as well.

Mullen said it was his sense that rank-and-file troops would support the change.

"I have served with homosexuals since 1968," Mullen said in response to questions from Republican Sen. Sessions. "There are a number of things cumulatively that get me to this position."