WASHINGTON — The Pentagon on Monday said it was unclear how soon the repeal of a ban on openly gay troops could be carried out after Congress scrapped the law in a ground-breaking vote.

Defense officials had to first review and revise policies and make other preparations to reflect the change adopted Saturday by the Senate, Pentagon press secretary Geoff Morrell told reporters.

"I don't think anybody has any idea yet how long this will take," Morrell said.

When President Barack Obama signs the measure into law -- the White House said this would be on Wednesday -- he will launch a White House and Pentagon certification process that could take months.

Once Obama, Defense Secretary Robert Gates and the chairman of the Joint Chiefs of Staff, Admiral Michael Mullen, certify that lifting the ban can be done without harming military readiness, effectiveness, unit cohesion, and recruitment, the change will enter into force within 60 days.

In the meantime, the 1993 "Don't Ask, Don't Tell" rule, which requires gays to keep quiet about their sexual orientation or face discharge, remains in effect, officials said.

Some gay rights groups have urged the administration to impose a moratorium on any further discharges under the law, but the Pentagon said it had no plans to adopt a freeze.

"Until 60 days after certification, 'Don't Ask, Don't Tell' remains in effect," Pentagon spokesman Colonel Dave Lapan said.

The Pentagon, however, raised the bar for any new discharges in October, making more expulsions unlikely under the current law.

In October, the defense secretary said no member of the military could be discharged under the law without approval of the secretaries heading up each branch of the armed forces, and in "coordination" with the personnel and legal chiefs at the Pentagon.

The department's general counsel, Jeh Johnson, said earlier this month that in carrying out the repeal, the Pentagon would need to strike a balance between moving too quickly or too slowly.

"I think the answer would be not fast, but not drawn out or protracted either. I think that it could become counterproductive for unit cohesion, good order and discipline if this process were drawn out over an extended period of time," Johnson said.