Jon Cooper, the majority leader of the Suffolk County legislature in New York, has announced he is considering whether to challenge US senator Kirsten Gillibrand in the Democratic primary in 2010.

Cooper, who is openly gay and has five adopted children, would be the first out senator if successful.

Speaking to Newsday, he said: “I consider myself progressive on the important issues,” alluding to gun control and gay rights.

“And obviously, Sen. Gillibrand has not been a strong supporter in the past on either issue.”

He added he is “very concerned” that state voters may lack confidence in a candidate who makes “a 180 degree turnabout” on major issues.

On the chances of him running for senator, he said: “It’s way preliminary right now, but I’ll have a better sense in a few weeks or perhaps the next few months.

“In a seven-way race, the winner doesn’t need 51 per cent, just 15 per cent.”