Any backtracking from Mr. Craig is not likely to go over well with Republican leaders. Within hours of the incident’s becoming public, the Senate leadership initiated an ethics inquiry, stripped him of his committee leadership positions and let Mr. Craig know he could face public hearings into his conduct if he chose to try to survive the furor.

A top Senate Republican aide, after hearing about Mr. Craig’s possible return Tuesday night, suggested that Mr. Craig was desperate.

“The people of Idaho and the rest of America were led to believe Senator Craig would resign,” said the aide, who spoke on condition of anonymity. “To go back on that intent means that he will only be a negative distraction for his colleagues. Like a fish out of water, he is gasping for his last breath of political air.”

Late Tuesday, Roll Call, the newspaper that covers Congress and first broke the story of Mr. Craig’s guilty plea, posted on its Web site an audiotape of a voice message the senator apparently intended for a lawyer of his, Billy Martin, on Saturday morning as he was heading to the news conference in which he announced his intention to resign. In the message, Mr. Craig indicated he could reconsider resigning.

“Arlen Specter is now willing to come out in my defense, arguing that it appears by all that he knows that I’ve been railroaded, all of that,” the senator said. “Having all of that, we’ve reshaped my statement a little bit to say it is my intent to resign on Sept. 30.”

Jon Hanian, a spokesman for Gov. C. L. Otter of Idaho, said Tuesday night that the governor learned that Mr. Craig was wavering on his resignation after a inquiry by a reporter about the possibility earlier in the day.

Mr. Hanian also said the possibility that the senator would reconsider his resignation “has been buzzing around the delegation.”