Richard June-Jorday Thomas, who had served five years of a maximum 20 for assaults on two young women in Tecolote Canyon in San Diego, Calif., was on his way to a therapy sessions for prison parolees on Aug. 1, 1975, when he took a detour through that same canyon.

Mary Ellen Martinez, 15, whose home bordered the canyon, was on her way home from summer school.

That afternoon, Thomas murdered Mary Ellen with a single thrust of a knife to her carotid artery. He was tried, convicted and sentenced to life imprisonment.

Stunned by the crime and by what they later heard about Thomas and his parole, the Martinez family sued California parole authorities for letting Thomas out of jail. In California, however, as in other states, the law gives those officials absolute immunity from such civil liability suits.

The Martinez family, in effect, couldn't get in the courthouse door.

Their confrontation with that absolute immunity statute has now reached the Supreme Court, which will hear arguements of it today. In legal terms, Martinez vs. California pits the right to redress against a doctrine designed to insulate parole officials, judges and prosecutors from both externally and self-imposed pressures as they decide people's fates.

In broader terms, something bigger is involved. The doctrine of absolute immunity is a cherished concept of "progressive" penology, at the heart of the idea of rehabilitation. It now confronts the growing rage of crime's victims, who feel, in the words of Mary Ellen's mother, "that it's all pretty rotten."

Here is the confrontation in the more refined words of the lawyers. On the one hand: "The strong societal interest in returning inmates to a useful life," says a friend-of-the-court brief filed in support of immunity by Alameda County, Calif., "required that members of the general public must bear the risk that the rehabilitative effort may fail. . . ." The Martinez family "has no constitutional right to be free from crime."

On the other: "The legal theory evidenced by the absolute immunity doctrine," states a brief on the Martinez side, " says that we must 'take a change' with the safety of society in order to vindicate the theory of rehabilitation.

"We can think of no more inportant issue, insofar as victims' rights are concerned, to come before this court," said Americans for Effective Law Enforcement Inc.

In the months after their daughter's murder, Mary Ellen's parents, George and Patricia Martinez, heard some things about Thomas that shocked them.

The judge at his previous assault trials had specifically warned that Thomas should never be paroled. He was too dangerous.

During his incarceration, psychiatrists at the Atascadero State Mental Hospital has classified him as a "medically disordered sex offender" who was not amenable to treatment.

Thomas' mother was active at low levels on political campaigns. The Martinez family heard that she got politicians to write to the parole authority on her son's behalf. Parole officials said they were unable to comment on that, but Thomas' lawyer said he, too, had heard talk of the efforts.

And the Martinez family heard that just weeks before the murder, Thomas had told authorities he feared what he might do. He was afraid he might lose control.

It was factors like these -- which have yet to be explained -- that the Martinez family hoped to resolve in court.

"George Martinez came to me with this sickened look on his face," recalls the family's attorney, Donald McGrath II. "They were so sickened by the loss of their child and the potential for others to lose children. They wanted me to do something, help them lobby, get in touch with a congressman.

"We said maybe this law, this immunity, shouldn't stand up."

So far, it has stood up. The California Court of Appeal upheld the unwillingness of the lower courts to hear the Martinez suit. "The stated purpose" of the immunity law, the court said, "is to allow correctional personnel to make determinations of release or parole unfettered by any fear . . . there is no liability here."

Maintenance of immunity is considered so important by government officials that several states, as well as the solicitor general of the United States, have filed briefs with the Supreme Court in support of it. To eliminate immunity, said the state of Ohio, "might well spell the end for the parole system still in its experimental stages."

"The prospect of a lay jury determining issues such as motivations and circumstances surrounding a parole official's decision to release a to be avoided," argued the state of California. It would "toll the beginning of the end of the parole system."

"The parole decision-making process," said the Ohio brief, "is a product of assessing imponderables and acting upon that assessment.

"Inherent in such a system must be the right to be wrong. The entire process lacks clear scientific laws and precise measurements . . . Rather, the system depends entirely on subjective evaluations utilizing the judgments of individuals who bring with them their experiences in life and the hope that their predictions are correct.

"Experience has taught us that often, these predictions are not correct."

McGrath said he had though at the outset that it was unlikely that the Supreme Court would take the case, though he held out the hope that the "severe facts" would serve as an impetus.

He also caught the court at the right time. The Burger court has upheld absolute immunity for judges and prosecutors, but it has eroded such immunity for other government officials.

The Martinez case is different from most of the others. The direct cause of their loss was not the state itself, but Richard June-Jordan Thomas. The state officials, while not prosecutors or judges, are part of the system the the Supreme Court has protected in other cases.

And the federal-state issues involved are complex, pitting the court's general dislike of immunity against its reluctance in recent years to interfere with the authority of the states.