Defense Secretary Robert Gates is warning troops that the law allowing gays to serve openly in the military is not officially in effect yet.

Though President Barack Obama has signed the law repealing the "don't ask, dont' tell" policy, the change is not expected to be in place for a number of months. The Pentagon issued a memo that Gates sent Wednesday night to armed forces branch heads and other officials explaining the timing and stressing that troops can still run afoul of the old law.

Aubrey Sarvis of the Servicemembers Legal Defense Network says the advocacy group has received dozens of phone calls from troops confused about the timing and wanting to make sure when they may legally begin talking about the fact that they're gay.