Illinois Gov. James R. Thompson today commuted the prison sentence of Gary Dotson to time already served, saying "no good purpose would be served" by returning him to prison. But he rejected Cathleen Crowell Webb's claim that she fabricated the rape charge that put Dotson behind bars six years ago.

"I am satisfied Dotson was proved guilty beyond reasonable doubt at his 1979 trial," Thompson, a Republican, said after reviewing the record of last week's three-day clemency hearing.

" But I have decided that no good purpose would be served -- that justice would not be served -- by returning Gary Dotson to prison," the governor added.

The decison frees Dotson, 28, from serving the remainder of his sentence of 25 to 50 years, provided he remains on good behavior for a period of time not yet set by the governor.

"I'm happy because I know I'm not going back to prison," the Associated Press quoted Dotson as saying at his family's home, where he watched the televised proceedings. "We're all going to sit around and get loaded."

Dotson, who has been free on bond since May 1, said he will continue trying to clear his name, either through a new trial or by continuing his appeal before an appellate court.

"I've still got a felony on my record that I want to clear," he said.

Thompson denied a pardon, saying Dotson failed to prove to him or the Illinois Prisoner Review Board that there was a "substantial likelihood of his innocence."

On the contrary, Thompson said, evidence that came to light during the clemency hearing "if anything . . . was stronger than at the trial." He said alibi witnesses for Dotson were "simply not convincing."

Thompson said the matter of clemency for Dotson "has nothing to do with guilt or innocence. It has to do with the larger quality of mercy, of compassion for one's fellow man."

In a formal statement this afternoon, Thompson called the clemency case "the most unique and difficult" one to come before him in eight years as governor but said, "I believe Webb was raped on the evening of July 9, 1977."

The governor, a former state and federal prosecutor, said he "did not believe" Webb's account that she fabricated the rape out of fear that she had become pregnant when David Beirne, who was then her boyfriend, completed sexual intercourse with her a week earlier.

On Saturday, Beirne testified that he and Webb had practiced coitus interruptus during every time they had intercourse.

Said Thompson: "There is no motive, eight years later, for him to lie."

The governor, who dominated the clemency proceedings, said he had reviewed thousands of pages of testimony from the trial and from hearings last month before Cook County Circuit Court Judge Richard Samuels, who presided at the original trial.

The new hearings were triggered when Webb emerged from obscurity in March to tell national television audiences that an innocent man was in prison because she had made up a rape charge in 1977.

Thompson said he does not believe her recantation. "I don't believe the testimony for the most part she gave here," he said at a brief news conference after he read his statement.

He said Webb's motive mystifies him. "I simply don't know. Like the state's attorney, like the trial judge, perhaps like all of you, I don't know with what intent she testifed at this hearing.

"I'm not even saying she committed perjury. Perjury requires a willful intent to lie. All I'm saying is, I don't believe the testimony because it was either inherently incredible or flatly contradicted by other witnesses who had no motive to lie and who were corroborated. And that's the most we can find."

He rejected Webb's assertion that scratches and abrasions found on her body after the assault allegedly took place were self-inflicted. He also said other parts of her recantation "were flatly contradicted by a number of witnesses who were unimpeached."

Thompson emphasized that he denied the pardon because he agrees with Judge Samuels and Cook County prosecutors that Webb was raped and that Dotson did it. "I think this record is perfectly capable of supporting a recommendation of no clemency at all," he said. "But I have to make a decision within the framework of what I think basic justice requires."

Webb's adamant assertion that Dotson be freed carried weight, Thompson said. "The views of the victim with regard to the sentence in this case are clear and are entirely separate from the question of the believability of her recantation."

He commuted the sentence, in part, he said, because Dotson would have been eligible for parole in three years. "Society has imprisoned Gary Dotson for six years. That's a long time. By my action, I am in effect taking three years off the normal sentence."

Dotson was seeking a new trial and appellate review of the original conviction. Thompson said he agrees with Samuels, who recently denied Dotson a new trial. Prosecutors had urged that Dotson be sent back to prison.

Carol Smith, Webb's foster mother, said she thought Thompson "made a very wise decision," the Associated Press reported.

"We have no objection to Dotson getting out of jail," said Smith, who has said she finds it difficult to believe that Webb was not raped. "I think he has served long enough."

The case has attracted national news coverage. Hundreds of spectators jammed last week's clemency hearings. Local television stations carried Thompson's news conference live today.