President Barack Obama has ended the ban on gay's in the US army. The US president and the Pentagon’s top two leaders today signed the required certification attesting that the Defence Department is prepared for repeal of the military’s ban on gays serving openly.

According to a law passed in December, the ban should be lifted ‘‘once and for all’’ 60 days after the certification, Obama said. Defence Secretary Leon Panetta and Navy Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, also signed the certification, which was sent today to lawmakers in Congress.

‘‘As of September 20, service members will no longer be forced to hide who they are in order to serve our country,’’ Obama said in a White House statement. ‘‘Today, we have taken the final major step toward ending the discriminatory 'Don’t Ask, Don’t Tell' law that undermines our military readiness and violates American principles of fairness and equality.’’

Obama campaigned on a pledge to repeal the 17-year-old prohibition, which dates to the administration of President Bill Clinton. More than 14,000 service members have been discharged for being gay since 1993, according to Servicemembers Legal Defence Network, which has worked for repeal.

Discharges under the law will end starting September 20 and personnel who were discharged under the ban will be allowed to re-apply to enter military service, said Marine Corps Major General Steven Hummer, chief of staff for the team charged with implementing the repeal.

The Defence Department has revised policies in preparation and conducted training sessions of 45 minutes to 90 minutes for 1.98 million of 2.2 million active-duty personnel worldwide since the law’s passage in December that laid the groundwork for the repeal.That was enough for the services to certify that they were ready for repeal, Hummer said. Remaining training and policy revisions will be conducted in the next two months, he told reporters at the Pentagon.

Chiefs of the individual military services supported certification unanimously, said Doug Wilson, a Pentagon spokesman. Panetta, who took office July 1, said the planning process ‘‘was designed to ensure the smoothest possible transition for the US military to accommodate and implement this important and necessary change.’’

Mullen helped sway Congress last year to repeal the ban by saying at a Senate hearing, ‘‘I cannot escape being troubled by the fact that we have in place a policy that forces young men and women to lie about who they are.’’

Today, he cited the training and policy review and a study that preceded those steps in saying the armed forces are ready for the change.