Washington ? Top Army and Air Force officers said Tuesday they would be reluctant to overturn a 17-year policy that prohibits gays from serving openly in the military without more time to ascertain it won’t hurt the services.

“I do have serious concerns about the impact of a repeal of the law on a force that is fully engaged in two wars and has been at war for eight and a half years,” Army Chief of Staff Gen. George Casey told Congress. “We just don’t know the impacts on readiness and military effectiveness.”

As Casey cautioned the Senate Armed Services Committee against moving too fast, Air Force Chief of Staff Gen. Norton Schwartz made similar remarks before the House.

The carefully crafted comments indicate reluctance among the military’s senior ranks to act anytime soon on President Barack Obama’s plan to repeal the “don’t ask, don’t tell” policy.

Obama says the policy is wrongheaded and should change. Defense Secretary Robert Gates agrees but wants to move slowly, and has ordered a lengthy assessment on how to lift the ban without affecting troops and their families.

Officials expect the study to be complete by the end of the year, but it could be several more years before the repeal is fully implemented.

In the meantime, congressional Democrats are debating how to advance the issue. Some party members are reluctant to repeal the 1993 law, while others want an immediate moratorium on dismissals.

The testimony by the service chiefs is considered crucial. As the top uniformed officials in each service, the chief is in charge of recruitment and preparing troops for deployments. If the policy on gays is overturned, they would have to decide how to implement the changes.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, already has said he thinks the law should be changed because it forces gay troops to compromise their integrity by lying about who they are.

On Wednesday, lawmakers will hear from Marine Corps Commandant Gen. James Conway, who is said to be an opponent of lifting the ban, and Adm. Gary Roughead, who is chief of naval operations.

At Tuesday’s hearing, Schwartz said he was concerned there is “little current scholarship on this issue” and wants to wait until Gates finishes his assessment.

Aubrey Sarvis, executive director of the Servicemembers Legal Defense Network, which advocates to repeal the law, said it’s important to note that Casey and Schwartz didn’t oppose Gates’ study on how a repeal would be implemented.

“There will continue to be differences around the margins, but at the end of the day, I think the chiefs will salute” the president and other leadership, Sarvis said.

Casey said he would oppose legislation being considered by Sen. Carl Levin, the committee’s Democratic chairman, that would force the military to immediately suspend dismissals.