The Supreme Court yesterday told California to stay out of Arkansas' business.

The justices, ruling in a case that had become a cause celebre among many social activists, said the California courts could not order an investigation of Arkansas' prison system before deciding whether to return an Arkansas prison escapee.

The California Supreme Court had done that after the escapee, serving a prison term for conviction of murdering a Little Rock policeman, contended that his life would be jeopardized because of the "cruel and inhuman" conditions and threats to his safety in the Arkansas prisons.

James Dean Walker, the escapee, successfully enlisted the support of prison reform advocate Jessica Mitford and former Arkansas prison warden Thomas Murton, the model for Robert Redford in the film "Brubaker," and obtained an order requiring the sheriff of El Dorado County, California, to "conduct hearings" on Arkansas prison conditions before returning Walker.

States ordinarily fully cooperate with other states in the return of escapees, the justices said yesterday in an unsigned three-page opinion (Pacileo vs. Walker). Justice Thurgood Marshall dissented. "Claims as to constitutional defects in the Arkansas penal system should be heard in the courts of Arkansas, not those of California," the justices wrote.

In fact, a federal judge held the Arkansas prison system unconstitutional 10 years ago, after reports of extreme brutality and medieval conditions in the prisons. While Arkansas has since made major changes in its prisons, Walker and his supporters argued that they were "cosmetic."

In other action yesterday:

The court agreed to decide whether Hustler magazine publisher Larry Flynt should stand trial in Ohio on obscenity charges (Flynt vs. Ohio). Flynt, a frequent unsuccessful Supreme Court petitioner, charged that Cleveland discriminated against his magazine, singling it out for prosecution from similar publications in an unconstitutional manner.

The July 1976 charges stemmed from citizen complaints about a Hustler cartoon showing sexual activity among President Ford, Secretary of State Henry A. Kissinger, Vice President Rockefeller and the Statue of Liberty. Hustler lawyers contended that numerous other "national men's magazines widely sold throughout the area" had formats similar to Hustler's and were not prosecuted.

The court let stand the Environmental Protection Agency's air quality standards for the control of lead in the atmosphere. The lead industry (Lead Industries Association vs. EPA) argued that the agency had not shown a firm medical consensus demonstrating that lead exposure was "clearly harmful to health."

The industry argued that last year's Supreme Court decision regarding exposure to benzene in workplaces required the showing of such a consensus.

In another lead-related matter, the court agreed to postpone imposition of Occupational Safety and Health Administration requirements for exposure to lead in plants and factories, pending a Supreme Court decision on whether to review those requirements.

The court agreed to decide what sort of records government contractors must provide to federal auditors as a condition of the contracts. The case (Staats vs. Bristol Laboratories) stemmed from the company's refusal to provide data concerning costs of research, development, marketing, promotion and distribution costs which the government wanted in order to study a Bristol contract for sale of pharmaceuticals to the Veterans Administration and the Pentagon.