A conservative US state senator who has voted against gay rights measures during his 14 years in office has confessed he is gay.

Republican Roy Ashburn came out during a radio interview in California, where he sits on the state legislature.

He has been on leave since his arrest last week on suspicion of driving under the influence.

Ashburn said his votes reflected the way his constituents wanted him to vote, not his own "internal conflict".

"I am gay... those are the words that have been so difficult for me for so long," the 55-year-old divorced father-of-four told KERN radio.

Ashburn said he felt the need to address rumours that he had visited a gay nightclub before his arrest on suspicion of drinking and driving in Sacramento on 3 March.

Last year, Ashburn opposed a bill to establish a day of recognition to honour murdered gay rights activist Harvey Milk.

He has also voted in the statehouse against efforts to expand anti-discrimination laws and recognize out-of-state gay marriages.

Ashburn, who represents California's 18th district, said he does not plan to run for any public office after his term ends later this year.