The Pentagon is set to certify later today that lifting the ban on openly gay troops will not harm the military.

This means that gay military personnel will be able to be open about their sexuality at the end of September, as the change does not come into affect until 60 days after certification.

Two weeks ago, military chiefs confirmed that lifting the ban would not affect military readiness. Defence secretary Leon Panetta will announce the decision later today, officials said.

Last December, a bill to repeal the 1993 law was approved by Congress and signed by President Obama. The bill stipulated internal research on how the military would adjust and training for troops.

More than 13,500 troops have been discharged since the law, known as Don’t Ask, Don’t Tell, began. It meant that gay troops could not reveal their sexuality and and senior officers could not ask them about it. However, troops could be fired if outed by a third party.

In his 2008 election campaign, Mr Obama pledged to repeal the law.

Attempts have been made to hasten the end of the ban. Earlier this month, the Ninth US Circuit Court of Appeals ordered the Pentagon to cease enforcing the ban after a court case brought by gay rights campaigners.

The Justice Department responded by asking the court to reconsider its verdict to “avoid short-circuiting the repeal process”.