A federal jury awarded $10.5 million in damages today to the relatives in Karen Silkwood, the young plutonium plant worker whose celebrated case began with her mysterious death almost five years ago.

The negligence judgment against her employer, the Kerr-McGee Co., came in an unprecedented suit alleging radioactive contamination outside a nuclear facility. It could thus become a landmark case in any future damage claim by nuclear workers or citizens exposed to radiation.

But perhaps more importanly, in another blow to the nation's nuclear industry, the jury's decision was a rejection of federal radiation safety standards and industry safety claims. It represents the first citizens' verdict on issues historically settled between the atomic industry and generally friendly U.S. government agencies.

Gerald Spence, the main Silkwood attorney, declared that the case showed "the government standards are baloney, a numbers game. They are not ture, and they don't protect the American public or nuclear workers." Spence, who had attacked federal regulatory agencies as "climbing into bed" with the industry, said. "The jury kicked industry and the government out of that bed."

Kerr-McGee attorneys said that would appeal the decision. Lead corporate attorney Bill Paul said, "Of course I'm disappointed - more than that, shocked and dismayed. If the appellate court upholds, it would mean each individual jury in each case becomes the standards setter, and the government regulations are no more than an opinion."

The Silkwood trial, spanning 11 weeks, was played out against a back drop of publicity unfavorable to the nuclear power industry, including the Three Mile Island power plant accident and the movie "The China Syndrome." Federal Judge Frank Theis had ordered the jurors to ignore both.

It was an emotional scene today. Silkwood supporters stood and cheered the verdict as the six-person jury filed out of the large ceremonial courtroom in the federal building here. More than 200 persons had jammed in to witness the climactic moment of a case that unified labor, feminist, civil liberties and environmental groups under one name: Silkwood.

A lab analyst at Kerr-McGee's old Cimarron plutonium fuel rod plant, Karen Silkwood reported for work contaminated with radiation on three sucessive days in November 1974. At that time, she was active in labor organizing efforts at the plant and in contract negotiations.

Eventually, the source of the radiation was found to be plutonium in her refrigerator at home. Just how it got there has never been absolutely ascertained, but the jury's verdict rejected Kerr-McGee's contention that she put in there herself.

Not long after, Silkwood was killed when her car went off the road as she was driving to a meeting with a union official and newspaper reporter. During the meeting, she supposedly was to turn over incriminating evidence to unsafe conditions at the plant.

The Oil, Chemical and Atomic Workers Union contends that her car was forced off the road and that the evidence was stolen. Police called it a one-car accident. The crash and Silkwood's death were not an issue in the case.

At issue was the safety of the operation of the plutonium plant. The two views presented here of that operation were as strikingly different as the portraits Silkwood and othrs painted of Kerr-McGee and vice versa.

Former workers testified that safety and health concerns were lacking. They said plutonium spill resudue was commonly painted over rather than removed, cancer risks were never mentioned, the plant was forewarned of "surprise" federal inspections and plutonium was removed easily from the facility.

Corporate officials testified that safety and security were priorities at the plant and that it was in "substantial compliance with government regulations."

Spence, attorney for the Silkwood family, portrayed Silkwood as a "heroine who had a great message to deliver to the American people."

But Kerr-McGee lawyer Bill Paul depicted her as a mentally unstable person "furious" about reprimands, frustrated about an inability to find actual shortcomings and "pressured" by her union to produce evidence of hazards.

Judge Theis would not allow testimony about Silkwood's character, testimony that would have included allegations of drug involvement, sexual promiscuity and mental troubles that supposedly included suicide threats well before she was contaminated with plutonium.

The company claimed that any emotional trauma she suffered between her exposure and her death was caused by her union problems and not, as her family's lawyers contended, by the "terror in the night" that she eventually would die of cancer caused by plutonium contamination.

Scientiest disagree sharply on the effects of that contamination, some saying there was none, other testifying she was wed to cancer from the moment of exposure.

After 21 hours of deliberation that began Thuesday afternoon, the jury awarded the Silkwood estate - essentially her parents and three children by a marraige that ended in separation - $505,000 in actual damages and $10 million in punitive damages.

Part of the legal significance of the case, if it is upheld on appeal, would be on Judge Thes' ruling that such uses of plutonium are so inherently hazardous that Kerr-McGee could be held liable for damages regardless of whether the company was negligent.

"The liability arises out of the abnormal activity itself and the risk it creates of harm to those in the vicinity," he had instructed the jury.

He told them, too, that while govrnment safety standards are "entitled to a high degree of respect and belerf," they need not be "accepted as right or accurate if they defy human credence."

The muclear power industry has sought to divorce itself from the Silkwood case, saying the Cimarron plant was not typical of the industry. The plant, which was closed in 1975, was making plutonium fuel rods for an experimental government reactor, not uranium fuel cells for a commercial plant.

"Clearly we don't have a reason to believe this reflects on the industry at large," said Bill Perkins, a spokesman for the Atomic Industrial Forum in Washington, D.C. He acknowledged the verdict "will have a psychological and political impact."

That impact may in the end be the most important to the industry, for the widely publicized trial - with its testimony of sinister health effects, sloppy management and ineffective regulation - came precisely as the antinuclear movement went "national" from a series of scattered protests.

Anthony Mazzocchi, wice president of the Oil, Chemical and Atomic Workers Union, called the verkict "a vindication of Karen's efforts and proof positive that her claims to us about what was going on inside that plant were accurate. It's a milestone in making plants safer for workers as well as the public."

And a tearful mother, Merle Silkwood, said: "She was only trying to help."

The allegations were not unlike those made over Three Mile Island and the Nuclear Regulatory Commission's confusion in dealing with it.

"This is why the Karen Silkwood case is so important," said Carrie Dickerson, head of an Oklahoma group fighting the construction of a proposed nuclear power plant. "It brought out a lot of things that were repeated by the media - it educated the public to the problems of radiation."