A major prosecution witness failed to offer important evidence that could have aided Gary Dotson, who was convicted in the now-renowned Cathleen Crowell Webb rape case six years ago, a Washington Post inquiry shows.

Testimony by Illinois criminal scientist Timothy R. Dixon appeared to support Webb's claim, which she recently has recanted, that Dotson raped her.

But a review of forensic evidence, interviews with Dixon and other criminologists, and a study of the trial transcript cast doubt on the value of Dixon's testimony.

In addition, there are doubts about Dixon's statement at the trial that he did graduate work at the University of California at Berkeley. Although Dixon appears to have attended a two-day seminar on the campus in 1972, a records clerk said his name does not appear on the list of graduate students.

The questions add new twists to a case that erupted three weeks ago when Webb, 23, a New Hampshire homemaker and mother, emerged from obscurity to claim that she had fabricated her 1977 accusation of kidnap and rape in a Chicago suburb that led to Dotson's imprisonment six years ago.

Webb's dramatic about-face resulted in world attention and brief freedom for Dotson. But he was sent back to prison April 11 after the original trial judge rejected Webb's recantation. Dotson, 26, is eligible for parole in 1988. Thousands of people have sent clemency petitions to Gov. James R. Thompson (R), who has promised a quick response to avoid "any clouds on Illinois justice."

But a nationally known criminologist who is reviewing the case said that, in his opinion, there was a "gross misrepresentation" in the way the prosecution presented some of its evidence against Dotson.

"This man did not get a fair trial," said Edward T. Blake, a California specialist in analyzing blood and other body fluids. "I'm not convinced Dotson is innocent. But I am convinced of the shocking nature of the state's handling of this case."

The Post interviewed Blake several times by telephone.

Questions about the Dotson case first were raised by Rob Warden, editor of Chicago Lawyer, who made his files available to The Post. His investigative monthly published articles this week that outline his findings.

Dixon, a forensic scientist with the Illinois Department of Law Enforcement, testified at the 1979 trial that stains found in Webb's panties were seminal fluid from a "Group-B secretor," a person with rare, Type-B blood indicators traceable in his body fluids. Less than 10 percent of the U.S. Caucasian population are Group-B secretors.

Dotson is a Group-B secretor. The prosecutor as part of a summation to the jury used this fact to link Dotson to the rape that Webb now claims never occurred.

The transcript shows this exchange between the prosecutor and Dixon on the stain:

Q: What was the result of the test of the seminal material as to ABO [blood group] typing?

Dixon: The seminal material was from a Group-B secretor.

The transcript shows that the prosecutor again asked whether the stains were made by a "Group-B secretor."

"That is correct," Dixon replied.

Neither prosecution nor defense attorneys asked Dixon whether the stains could have come from a person of another grouping.

In his summation, assistant Cook County state's attorney Raymond Garza, a veteran prosecutor, declared: "Is it coincidental that when he ejaculated on her panties that semen was found to be Group-B type semen and he is a Group-B secretor? Is it coincidence or fact and corroboration? It is corroborated by her positive identification."

However, Dixon's laboratory reports showed that Webb is a Type-B secretor, like Dotson, and that her vaginal discharges, not necessarily Dotson's semen, could have caused the stain identification. Dixon did not mention this in his testimony. Moreover, Blake, in analyzing Dixon's lab reports, said there is no factual ground for Dixon to have characterized the panty stain as seminal material.

Dixon, in a telephone interview Friday from his office at the Illinois crime lab in Joliet, said that "almost anyone" could have been chemically linked to the stain that prosecutor Garza linked to Dotson.

"It could have come from Crowell Webb or Dotson or someone else," Dixon said. "It could have been a nonsecretor." Dixon mentioned other blood groupings that could have caused the stains.

"In other words, almost anyone in the entire population could have been the source," Blake said.

Asked why he had not offered this information at the trial, Dixon said, "I guess it just wasn't asked . . . . Usually, a defense attorney asks" such a question.

But in sharp contrast, another state forensic scientist, Mark Stolorow, did not hesitate recently to describe the difficulties of identifying the source of the panty stain.

Stolorow testified for the prosecution at the April 11 hearing triggered by Webb's recantation.

With Cook County Circuit Court Judge Richard L. Samuels presiding, assistant prosecutor J. Scott Arthur asked Stolorow to tell the results of new tests Stolorow had made of the panties and of fluids taken from Webb and Dotson.

Stolorow said: "The ABO Group-B and [Group-]H activity in the seminal stains in the panties could have originated entirely from Cathleen Webb herself, if the semen were deposited by a nonsecretor. Or it could have originated from the vaginal secretions of Cathleen Webb in combination with a Group-B secretor, or . . . from her vaginal secretions in combination with a Group-O secretor or some combination of semen from Group-O, Group-B, and/or [Group-]A nonsecretor."

Asked about the discrepancy between his brief answer and Stolorow's detailed answer to the question of the stain's origin, Dixon said identification techniques are more advanced than eight years ago when he began conducting his tests.

Dixon also suggested that although "basically accurate," the 1979 trial's stenographic transcript "may have distorted some things. They don't get it exactly. They summarize. Obviously, you'd be better off if they recorded it all."

"Nonsense," Blake said. "If you look at the sense of Dixon's testimony, there is grounds for a new trial. Dixon shouldn't have answered the questions the way he did. He does not have the evidence to support his statement about a Group-B secretor." Blake, who operates his own criminal-science lab, has been an expert witness at scores of trials, frequently for the prosecution.

Dixon's signed laboratory report on the stains mentions only "Group-B blood group substance . . . present in the seminal material."

Dixon analyzed stains, blood and hair found on Webb and her clothing after the alleged rape July 9, 1977.

Webb, who was 16, said two long-haired men had dragged her into a car as she was walking home after work at a fast-food restaurant 2 1/2 blocks from her house in Homewood. They drove aimlessly through darkened streets while one assaulted and raped her in the back seat, she said. She helped compose an artist's sketch of the alleged rapist and later picked Dotson from a police mug book and a lineup.

Now a born-again Christian living in Jaffrey, N.H., with a husband and two children, Webb says she concocted the story out of fear that she had become pregnant by a teen-age boyfriend. She said she never had seen Dotson until she picked his photo as the most similar to the police sketch made from her phony description. Webb's attorney says a privately administered polygraph test shows that her recantation is truthful.

Dixon, 40, has been a principal forensic specialist for Illinois for 15 years. He has a BS degree from Loris College in Dubuque, Iowa, and an education degree from Aurora College in Aurora, Ill. Trained as an Army medical lab technician, he served in Vietnam.

He testified that he "studied the separation of red blood-cell proteins and enzymes" in 1972 as a Berkeley graduate student.

But he "is not on any listing of students who ever attended" Berkeley graduate schools, a Berkeley records clerk said. Informed of this, Dixon blamed a filing error. "That's not unusual in this world. I was there. I got credit from UC Berkeley. I have a certificate. [The course] was somewhere between a week and two weeks."

According to other records, Dixon took a two-day course in blood-stain analysis from U.C. Extension, a continuing-education center on the Berkeley campus, which has no academic affiliation with the university