The extraordinary three-day clemency hearing in the Cathleen Crowell Webb rape-recantation case ended today with Illinois prosecutors demanding that Gary Dotson's bid for freedom be denied.

Cook County Assistant State's Attorney J. Scott Arthur said Dotson "is guilty of a vicious crime" and should not be pardoned or have his 25- to 50-year prison term commuted. Dotson has served nearly six years for a rape that his alleged victim now swears she fabricated.

Dotson's clemency plea is being considered by the 10-member Illinois Prisoner Review Board, which retired this afternoon to deliberate behind closed doors.

The board is to make a confidential recommendation to Gov. James R. Thompson (R), in whose hands Dotson's fate rests. Thompson, who dominated this hearing as chief interrogator of more than two dozen witnesses, is expected to announce his decision in several days.

Dotson, 28, was freed on bond last week pending appeals. Thompson could pardon Dotson on grounds of innocence, deny his petition for a full pardon but free him by commuting his sentence or deny clemency. If all of Dotson's appeals fail, he will go back to prison. He is eligible for parole in three years.

Prosecutor Arthur and an assistant challenged the heart of both Webb's recantation and Dotson's defense. They attacked what they call Webb's "selective memory" and said her "sexual experience" contradicted her claim that she feared pregnancy from having had intercourse with David Beirne, who is now an Air Force enlisted man. Her recantation, they asserted, "defies common sense; defies belief."

They said Dotson's alibi witnesses "couldn't get the story straight," deriding them as witnesses who were produced at various hearings "on the installment plan."

Today's hearing was punctuated by testimony from Beirne, who was Webb's boyfriend when they were teen-agers. His statement contradicted a key part of her recantation.

The hearing closed with the dramatic appearance of Dotson's widowed mother, Barbara, who declared, "I just know my son is innocent," then crossed the auditorium to embrace her son. Webb, sitting nearby, watched silently.

Before a near-capacity crowd of about 400 that included Nobel Prize-winning novelist Saul Bellow, Beirne disputed Webb's Thursday testimony that they once completed sexual intercourse.

She has said that the only time Beirne failed to practice coitus interruptus was the last time they had intercourse. She testified that, as a result, she feared that she was pregnant and fabricated the 1977 rape for which Dotson was convicted.

Under questioning by Gov. Thompson, Beirne said he and Webb engaged in oral sex and intercourse "five to 30 times" on summer weekends in 1977, when she was a 16-year-old high school student.

No birth-control devices were used, he said. Did he ever complete the act "inside her," Thompson asked.

"No."

Did Beirne "always interrupt before" completion, Thompson asked.

"Yes, sir," Beirne said.

The close questioning typifies Thompson's conduct throughout the three days of public testimony before the review board.

Dotson was convicted in 1979 of rape and kidnaping.

Dotson was released last week on appeals that Webb triggered when in late March she began recanting her allegation that Dotson had raped her Saturday, July 9, 1977.

Beirne said that he had met Webb in the seventh grade, in 1973-74, and that their sexual relationship began in 1977, on weekends when she visited her aged guardian, Nellie Landers, who lived near Beirne in Chicago's Homewood suburb.

Beirne recounted that he would tap on a side window and that Webb, wearing a nightgown, would let him in the front door. He would stay "three to five hours," having intercourse "more than once," he testified.

But Beirne said he "couldn't put a date" on the last time he and Webb had intercourse. "It could have been Friday," he said, although he was "not real sure." He said he could not remember having sex with Webb July 8, 1977, which was a Friday.

On July 9, suburban police found Webb hysterical and with her clothing disordered. She said she had been raped in the back of a car. Dotson was arrested the following week, when she identified him from a mug shot and in a police lineup.

Beirne's hazy recollection of the last time he and Webb had intercourse is important to Webb's recantation. She has said that she could have had sex with Beirne as many as six days before she reported the alleged rape.

On this point, Illinois forensic scientist Mark Stolorow testified today that he doubts whether semen found on Webb's pants July 9 could have come from intercourse that occurred more than 24 hours earlier.

Testifying in the darkened auditorium of the new State of Illinois Center, Stolorow projected slides of Webb's panties on a nine-foot-high screen and described the results of his tests. He said he found semen throughout a stain that stretched for 11 inches from the front of the panties almost to the rear waistband area, but he said he thinks that "the chances of finding a stain that size 24 hours after intercourse low or improbable."

Stolorow said blood-typing traced to the semen found in the panties "could have originated from Dotson or Beirne or any other of 66 percent of U.S. Caucasians or 78 percent of blacks."

In other testimony, James Zagel, a top Illinois law enforcement official, showed statistics indicating that persons convicted of rape and kidnaping serve an average of 5.4 years in Illinois prisons -- less time than Dotson has served.