UPDATE 3-Republican U.S. senator quits over sex scandal

(Adds White House comment, details, background)

By Deanna Darr

BOISE, Idaho, Sept 1 (Reuters) - Republican Sen. Larry Craig of Idaho, caught in a sex scandal that quickly lost him the support of his party after his arrest in a men's toilet, said on Saturday he would resign from the U.S. Senate.

Craig pleaded guilty to disorderly conduct last month after he was arrested in an undercover investigation of lewd behavior in an airport men's room.

"To Idahoans I represent, to my staff, to my Senate colleagues, but most importantly to my wife and family, I apologize for what I have caused. I am deeply sorry," Craig, 62, said at a news conference.

The three-term senator from the solidly Republican and sparsely populated state said he would step down on Sept. 30.

Craig's departure capped a week of turmoil for Republicans, already reeling from ethics problems, with the disclosure of his arrest.

Idaho Gov. C.L. "Butch" Otter will pick a successor to complete Craig's term, which runs through next year. He was expected to choose a Republican and maintain the current 51-49 Democratic control of the Senate.

Craig, who was elected to the Senate in 1990, is ending his career after the revelations on Monday of his guilty plea. He was arrested June 11 in the men's room at the Minneapolis-St. Paul airport, where police were targeting public sex.