WASHINGTON – Lawmakers this week will press the military’s top uniformed officers for the first time on whether they think repealing ”don’t ask, don’t tell” makes sense or would be too disruptive.

The testimony from each of the service chiefs on Capitol Hill will be crucial to the debate in Congress on whether to repeal the 17-year-old law, which bans gays from serving openly in the military.

President Obama says the policy unfairly punishes patriots who want to serve their country. Defense Secretary Robert Gates agrees and has begun a yearlong study on how to mitigate the impact of lifting the ban.

Providing much-needed political cover is the chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, who says he thinks the law unfairly forces gay troops to compromise their integrity by lying about who they are.

But lawmakers, who are divided on whether to end the ban, say they want to hear from the service chiefs. They are the ones who would be in charge of putting any changes in place and responding to any fallout.

”The armed forces have always placed military effectiveness above individual needs,” said Rep. Gene Taylor, a conservative Democrat from Mississippi who says he is unconvinced that the ban should be lifted. ”This is one of the core concepts that has made the U.S. military one of the most effective combat forces in history.”

While Mullen says he believes the ban should be lifted, he has said he can’t speak for the service chiefs other than to say they support Gates’ yearlong assessment.

The service chiefs are scheduled to testify separately throughout the week, with the Army’s Gen. George Casey and the Air Force’s Gen. Norton Schwartz going first Tuesday. Marine Corps Commandant Gen. James Conway, who is said to oppose changes to the policy, will testify Wednesday.

”We believe that any implementation plan for a policy permitting gays and lesbians to serve openly in the armed forces must be carefully derived, sufficiently thorough and thoughtfully executed,” Mullen told a Senate panel last month.

The testimony of the service chiefs is considered so critical to the debate that House lawmakers have asked that they appear twice. In addition to this week’s testimony, which is supposed to focus primarily on the 2011 budget, the House Armed Services Committee wants the chiefs to return for a separate hearing dedicated solely to the military’s policy on gays.

”We strongly urge that no impediments be placed or erected to forestall that appearance or inhibit their testimony,” a group of Republicans, led by Rep. Buck McKeon of California, wrote Gates and Mullen.

According to a February Pew poll conducted after Mullen’s testimony, 61 percent of those questioned said they favor allowing gays to serve openly while 27 percent said they were opposed and 12 percent said they didn’t know.

Pew research has found that support for letting gays serve openly has risen from just over half of all those surveyed in 1994 to 58 percent in 2005 and about 60 percent since 2006. Opposition has dropped from 45 percent in 1994.

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