The US Supreme Court has handed President Donald Trump a victory on his policy barring many transgender people from the military, lifting lower court rulings that had blocked it on constitutional grounds from going into effect.

The decision, with the court’s five conservative justices prevailing over its four liberals, granted the Trump administration’s request to put on hold injunctions issued by federal judges against enforcement of the policy while a challenge to its legality continues in lower courts.

The court did not resolve the underlying question of the legality of the Republican President’s plan. Mr Trump’s decision reversed the landmark 2016 policy of his Democratic predecessor, Barack Obama, to let transgender people for the first time serve openly in the armed forces and receive medical care to transition genders.

But in lifting the injunctions, the court signalled it likely would decide in favour of the administration when it eventually is asked to rule on the merits of the challenge brought by transgender people already in the military or hoping to join.

The plaintiffs argued the policy violated the US Constitution’s guarantee of equal protection under the law.

The justices declined the administration’s request to immediately take up the fight about the policy’s legality, even before a ruling on the issue by a California federal appeals court that often has been criticised by Mr Trump.

Lawyers for the plaintiffs condemned the court’s action and said some current troops could face discharge. Various injunctions had allowed new transgender troops to join the military as of January 1, 2018, in addition to the estimated thousands already serving.

The US military allowed gay troops to serve openly for the first time from in 2011 under Mr Obama.

“For more than 30 months, transgender troops have been serving our country openly with valour and distinction, but now the rug has been ripped out from under them, once again,” said Peter Renn, a lawyer for Lambda Legal, which represents some of the plaintiffs.

House of Representatives Speaker Nancy Pelosi, a Democrat, said Mr Trump’s “ban on trans Americans serving in our nation’s military was purpose-built to humiliate brave men & women seeking to serve their country”.

In 2017, Mr Trump announced a plan to ban transgender people from the military, citing the “tremendous medical costs and disruption” of having transgender troops.

-AAP