Army Chief of Staff General George Casey says he is concerned about attempts to repeal the Don't Ask, Don't Tell policy that bans gays from openly serving in the military.

"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," Casey told a Senate panel this week. "We just do not know the impacts on readiness and military effectiveness."

However, President Barack Obama says the policy should be changed. Defense Secretary Robert Gates agrees, but wants to move slowly, and has ordered an assessment on how to lift the ban without it having an affect on troops and their families.

Officials expect the study to be complete by the end of the year, but the repeal would not completely take effect until several years later.

Meanwhile, the Pentagon is reviewing the policy at the request of President Obama.