The US Food and Drug Administration (FDA) says it will lift a decades-old ban on gay and bisexual men donating blood.

Gay men will be able to donate blood one year after their last sexual contact, the FDA said, under a proposal that will be introduced early next year to end a ban that has been in place since 1983.

The ban was first imposed at the height of the AIDS epidemic - a time when little was known about the virus, and testing was unreliable.

The ban prevented men who identified as gay or bisexual from ever donating blood.

Now, the FDA, after "carefully examining and considering the available scientific evidence", has said it would lift the lifetime ban.

There would still be a restriction on men who have had sex with other men in the previous 12 months, as there is in Australia and European countries.

The FDA said it hoped to issue draft guidance on the policy early next year.

It would then review the comments and issue final guidance "as quickly as possible," said Peter Marks, deputy director of the FDA's Centre for Biologics Evaluation and Research.

Scientific evidence showed the move would not create risks for the nation's blood supply, the FDA said.

The policy change is expected to boost the supply of donated blood by hundreds of thousands of litres per year.

The FDA said the move aligned the policy for gay men with that for other men and women who were at increased risk for HIV infection.

Gay rights groups said the change was long overdue.

The move is expected to lift US blood stocks by around 4 per cent.