Obama's signature would end the Pentagon's 17-year, "don't-ask, don't tell" policy and fulfill a 2008 presidential campaign promise.
The policy has allowed gays and lesbians to serve, but only if they were silent about their sexual orientation.
Press secretary Robert Gibbs would not say how long it would take for the administration to implement the repeal. But he said he didn't expect it to be "overly burdensome."
Gibbs declined to offer advice to gays now serving, or to those who've been discharged and want to reapply, citing a review of those questions by lawyers.