Amid intense pressure from his colleagues and the national Republican Party, Sen. Larry E. Craig’s office said the senator planned to make a Saturday announcement.

Senior GOP aides on Capitol Hill said a number of Craig’s GOP colleagues and officials of the Republican National Committee have let Craig know they want him to resign and relieve his party of a political burden going into the 2008 election.

Jon Hanian, spokesman for C.L. “Butch” Otter, the state’s Republican governor, said the governor had spoken with the senator but provided no details of the phone call.

Otter would select someone to serve out the remainder of Craig’s term, should Craig choose to resign.

Otter’s office was silent on the successor he would appoint if Craig resigns, but several candidates began angling for the job.

Lt. Gov. Jim Risch was already expected to run in 2008, but he could face competition from Rep. Mike Simpson, R-Idaho, a former speaker of the state House. “Rep. Simpson would be a contender for that role. He could hit the ground running,’’ said Nikki Watts, a spokesman for the five-term lawmaker. Simpson is an appropriator and a close advisor of Minority Leader John A. Boehner, R-Ohio.

Another potential candidate, Bill Sali, R-Idaho, bowed out this week. “The congressman doesn’t have any interest in the Senate seat,’’ said Wayne Hoffman, a Sali spokesman.

Earlier this week, the three-term senator from Idaho gave up positions of authority on three legislative committees. He additionally was facing an Ethics Committee investigation into the circumstances that led him to plead guilty to disorderly conduct — a charge spurred by a combination of hand and foot motions that an undercover police officer in the Minneapolis-St. Paul International Airport interpreted as an invitation for sex.

Craig told the officer his actions meant nothing of the kind and suggested he was the victim of entrapment. “I am not gay. I never have been gay,” he said earlier this week, explaining that he chose to plead guilty and keep the arrest secret from the Senate, his family or any lawyers “in the hope of making it go away.”

Craig’s colleagues in the Senate — including some who have served with him for 17 years and even before that, in the House — have both privately and publicly clarified that they want the issue to go away before it damages Republican prospects in the 2008 elections.

The GOP leadership told Craig that if he returned to work, it would be without any vestige of authority; they demanded that he step aside as the top Republican on one full committee and on an influential Appropriations subcommittee.

“This is not a decision we take lightly but we believe this is in the best interest of the Senate until this situation is resolved by the Ethics Committee,” said a joint written statement from GOP Leader Mitch McConnell and his top lieutenants.

In off-the-cuff remarks to the Lexington Herald Leader Aug. 30, Senate Minority Leader Mitch McConnell criticized Craig’s conduct in the Minneapolis airport incident as “unforgivable.”

“We have acted promptly to begin the process of dealing with this conduct,” he said. “We will see what happens in the coming days.”

GOP aides said McConnell was incensed that Craig had not notified him or other colleagues about his guilty plea.

Soon after learning of Craig’s arrest and guilty plea, McConnell convened a conference call of a half-dozen Senate GOP leaders on Aug. 28. They decided to immediately call for an investigation by the Senate ethics committee of Craig’s conviction.

Shortly afterward, McConnell and his colleagues watched on television as a defiant Craig described his intention to fight the conviction and hinted at aggressive efforts to save his career. His apology for pleading guilty and failing to notify his family, friends and colleagues — not for any criminal act — stunned senior Republicans, GOP aides said.

Craig’s arrest happened June 11, in an airport rest room not far from a food court. He signed the guilty plea on Aug. 1, and mailed it to Minneapolis, where it was recorded in court on Aug. 8. The episode remained secret until a Capitol Hill reporter was tipped to it, and the news broke on Aug. 27.

The news triggered a series of damage-control meetings by Republicans in Washington and Idaho, who watched as the stink about the Craig arrest became a primary source of late-night television comedy.

In the plea agreement Craig stated, “I understand that the court will not accept a plea of guilty from anyone who claims to be innocent. . . I now make no claim that I am innocent of the charge to which I am entering a plea of guilty.”

Craig said he did not consult a lawyer before pleading guilty, but this week he hired a local expert: Chris Renz, a former prosecuting attorney for the Metropolitan Airports Commission in Minneapolis.

Bart Jansen contributed to this story.

First posted Aug. 31, 2007 2:16 p.m.