Karen Silkwood: Was it murder?; The Killing of Karen Silkwood: The Story Behind the Kerr-McGee Plutonium Case, by Richard Rashke. Boston: Houghton Mifflin Company. $12.95.

More than six years after she was killed in a mysterious and perhaps sinister auto accident in Oklahoma, Karen Silkwood is still a symbol of the bitter controversy over nuclear power.

A jury last year determined that the young nuclear technician indeed had been deliberately contaminated with plutonium and that the Kerr-McGee Corporation was negligent in protecting the health and safety of its workers. In a narrow sense , she has been vindicated.

But this riveting book gets beyond the surface facts and simple emotions of the Silkwood case to the fundamental and in some cases frightening aspects of a story that may never be completely told.

Was Silkwood's death not an accident but part of a conspiracy? What about the obviously questionable actions of law enforcement agencies, including the FBI? Why were the CIA and other national-security agencies so interested in the case? Did it have anything to do with plutonium stolen by foreign agents or secreted to friendly countries for weapons production?

Like the good investigative reporter he is, Rashke draws on congressional and court documents, eyewitnesses and participants, and inside sources to lay out a scenario that is as fascinating and gripping as anything John le Carre or Agatha Cristie could devise. Unfortunately, since he is dealing with devilishly limited facts, Rashke must leave the reader to decide "whodunit."

One hopes that subsequent investigatory work will provide more complete answers. If anything, this book clearly shows that those who should have been finding those answers --courts -- have not done their job.

Throughout the book, one gets the sense that Karen Silkwood was the victim of more than just an unexplained car crash. She was used by her employers to stifle union activities, by her own union to strengthen its position, by ambitious lawyers, by the women's movement at a time when it was divided and needed a cause, and by the press.

She was also a victim of her own weaknesses. Rashke adds to his credibility in not glossing over such things as Silkwood's drug use or the fact that she may indeed (as critics have claimed) have been smuggling materialout of the Kerr-McGee plant to further her union's aims. She would not be a neat heroine for a Jane Fonda movie.

After Silkwood's death (and more recently the accident at Three Mile Island), some improvements have been made in the nuclear industry, particularly in the way it is regulated.

"The Killing of Karen Silkwood" is a grim but necessary reminder that the questions about nuclear safety may st ill outnumber the answers.