Instruction 1332.38 on disabilities in the US military classes being gay under the same heading as mental retardation, personality disorders and alcoholism.

A group of 10 congressmen have written to Defence Secretary Donald Rumsfeld asking that "inadvertent outdated language" be updated.

The Pentagon says the list, which was re-certified in 2003, is under review.

'No scientific basis'

Marty Meehan, Democratic representative for Massachusetts, and nine other members of the Armed Services Committee sent the letter on Tuesday.

The document's list of "mental disorders" includes homosexuality

"It is disappointing that certain Department of Defense instructions include homosexuality as a 'mental disorder' more than 30 years after the mental health community recognised that such a classification was a mistake," Mr Meehan said.

"There is no scientific basis for such a classification which leads me to believe that the classification is motivated by something more sinister."

The letter points out that two other Department of Defense regulations on mental health do not include homosexuality on any lists of psychological disorders.

It requests that all Pentagon regulations be adapted in keeping with the American Psychiatric Association's stance that "homosexuality per se implies no impairment in judgment, stability, reliability, or general social and vocational capabilities".

'Don't ask, don't tell'

The lawmakers also called for a complete review of the US military's policies and medical regulations, in order to meet the needs of what they estimated to be about 65,000 homosexual and bisexual members of the US armed forces.

The document was uncovered by the Center for the Study of Sexual Minorities in the Military, at the University of California at Santa Barbara and is posted on the group's website.

Under the current "don't ask, don't tell" policy, the US military is prohibited from asking about the sexual orientation of its members, but must discharge those who are openly homosexual.

Replacing the 10,000 homosexual soldiers forced to leave the US army in the last 10 years has cost $200m (£106m), according to a report released last year by the US Government Accountability Office.