Barack Obama to sign gay military law after 17-year ban

Over 13,000 service members have been dismissed under the policy. It was enacted under President Bill Clinton in 1993 as a compromise.

Opponents argue that the change will damage troop morale at a time of war. However, earlier this month, a Pentagon report said that allowing openly gay troops would have little impact on the cohesion of US forces fighting in Iraq and Afghanistan.

The outgoing Senate and House of Representatives approved the new law last week, with moderate Republicans joining the Democratic majority.

A large turnout of activists is expected at the signing ceremony; the White House has booked a larger room for the event. But planned celebration parties by gay rights campaigners and military members may be premature as guidelines still need to be finalised on practical questions- namely how to educate troops and how sexual preference should be handled when army staff are organising sleeping arrangements in military barracks.

Those guidelines need to be signed off by President Obama, Defence Secretary Robert Gates and Admiral Mike Mullen, chairman of the Joint Chiefs of Staff.

The new law will officially take effect another 60 days after the signing. Until then, the current ban remains in place.