Craig will announce at a news conference in Boise Saturday morning that he will resign effective Sept. 30, four state GOP officials said, speaking on condition of anonymity.

The announcement follows by just five days the disclosure that he had pleaded guilty Aug. 1 to a reduced misdemeanor charge arising out of his arrest June 11 at the Minneapolis airport.

The three-term Republican senator had maintained that he did nothing wrong except for making the guilty plea without consulting a lawyer. But he found almost no support among Republicans in his home state or Washington.

Idaho Gov. C.L. "Butch" Otter appeared Today to have already settled on a successor: Lt. Gov. Jim Risch, according to several Republicans familiar with internal deliberations.

Craig has been out of public view since Tuesday, but Republican sources in Idaho said he spent Today making calls to top party officials, including the governor, gauging their support.

There has been virtually none publicly.

Asked Today at the White House if the senator should resign, President Bush said nothing and walked off stage.

Republican officeholders and party leaders maintained a steady drumbeat of actions and words aimed at persuading Craig to vacate his Senate seat.

GOP lawmakers, hoping to get the embarrassment to the party behind them quickly, stripped Craig of leadership posts on Wednesday, one day after they called for an investigation of Craig's actions by the Senate Ethics Committee. Craig complied with the request.

With his wife, Suzanne, at his side, he said he had kept the incident from aides, friends and family and later pleaded guilty "in hopes of making it go away."

Craig, 62, has represented Idaho in Congress for more than a quarter-century and was up for re-election next year.

Republican officeholders and party leaders wanted Craig to give up his seat in the Senate as soon as possible. Their preference, according to several officials, was for a successor to be selected and ready to take the oath of office when the Senate returns from its summer vacation next week.

Senate Minority Leader Mitch McConnell called Craig's conduct "unforgivable" and acknowledged that many in the rank and file thought Craig should resign.

Republicans, worried about the scandal's effect on next year's election, suffered a further setback Today when veteran Virginia Sen. John Warner announced he will retire rather than seek a sixth term. Democrats captured Virginia's other Senate seat from the GOP in the 2006 election and have sought to line up former Gov. Mark Warner to run if the seat became open.

The contest for control of the next Senate was already tilted against Republicans, who must defend 22 of 34 seats on the ballot next year, before the Craig scandal and Warner's announcement.

With a GOP candidate other than Craig, Republicans would stand a much better chance of keeping his Idaho seat in 2008.