BOOK REVIEW : Klan and FBI Wounded in Hail of Bullets : TERROR IN THE NIGHT: The Klan’s Campaign Against the Jews By Jack Nelson : Simon & Schuster $22; 304 pages

When Kathy Ainsworth’s husband learned that his wife had been killed in the summer of 1968, he told a news reporter over and over again that “She was just an angel, an angel.”

To outward appearances the description seemed fair, for Ainsworth was a fifth-grade teacher, the organizer of a school cookbook to which she contributed recipes for fig cake and Brunswick stew.

After her death, however, Kathy Ainsworth’s reputation changed: She had been killed in a hail of police bullets, waiting in a car while her lover, a fellow member of the Ku Klux Klan named Tommy Tarrants, attempted to bomb the home of a prominent Jewish citizen of Meridian, Miss.

It would make a good story--how run-of-the-mill Southern racism metastasized in a bright, religious college graduate until it became a vicious, messianic creed holding blacks, Jews, and Communists responsible for most of the nation’s ills.

But Ainsworth’s tale is only a sidelight in “Terror in the Night,” for Jack Nelson, Washington bureau chief of the Los Angeles Times, has written this book not to chronicle Ainsworth’s transformation but to set the record straight.

Nelson covered the story for the Los Angeles Times just as the authorities told it--the headline to his 1968 Page 1 story read “Mississippi Police Thwart Dynamiting: One Dead, One Wounded”--but months later learned that Ainsworth and Tarrants were shot while participating in a sting operation set up by the FBI and local police with information paid for by the Jewish community.

In 1970 Nelson published in The Times a detailed description of the entrapment, thus ensuring his position near the top of J. Edgar Hoover’s enemies list. The article gave the general outlines of the story told in this book--how law enforcement authorities were willing to break the law, and even to kill, in order to do their job as they saw fit.

But it’s easy to see why the case has stayed with Nelson all these years, and why he wanted to write about it yet again: Simply put, it confounds the conventional distinctions between right and wrong.

Entrapment by law enforcement officials is easy to deplore, but the way Nelson frames the story it’s difficult to finish “Terror in the Night” without concluding that the police and FBI, considering the time, the place and the people involved, may have done just the right thing.

Nelson, who grew up in Mississippi, comes to no such conclusion himself. But he does lay out the seeming inevitability of the entrapment plan, which evolved from an unusual confluence of circumstances; the dearth of leads identifying the perpetrators of an anti-Semitic bombing wave, the almost religious conversion of Meridian police chief Roy Gunn to color-blind law enforcement, the willingness of Southern Jews to put up significant reward money and the continuing national focus on Mississippi since the infamous 1964 murder of three civil rights workers, and Hoover’s subsequent war on the KKK through the massive use of Southern FBI agents.

One wonders, absent any of these factors, whether the entrapment plan would have come to pass.

Although the Klan has always been anti-Semitic, it turned to regular terrorism against members of the faith only after activist Jews--usually from the North, since many Southern Jews were themselves segregationists--became involved in the civil rights movement.

When the FBI recorded one Klan meeting in which a member suggested bombing an occupied synagogue regardless of who was inside because “Little Jew bastards grow up to be big Jew devils,” and learned that both Gunn and two FBI agents were on a Klan assassination list, it became clear the KKK was nearing a state of frenzy.

With money already raised through B’nai B’rith and the Anti-Defamation League to elicit information against the Klan, it must have seemed, at the time, only a small step for Gunn to ask whether the ADL would object to the reward money being used to “to purchase bodies and not testimony.”

If the police and FBI had known their trap would result in the death of a female teacher, even if she was also a Klan terrorist, there’s little question the plan would have been abandoned.

It was Tarrants, a careful, cold-blooded bomber, they were after: As one officer told Nelson, “We had in mind killing him, I don’t mind telling you.”

But why did such extra-legal killing seem necessary?

Partly, it seems, to protect informants, who had received more than $20,000 in reward money, but mostly because Southern law officials--their ability to enforce the law challenged--wanted to teach the Klan a lesson.

And whether one agrees with the methods used or not, the lesson took: The Tarrants-Ainsworth entrapment, according to FBI files, “broke the back of the Klan in Mississippi.”

“Terror in the Night” is fascinating journalism, a tale with two plots--first, of the attempted bombing, and second, of Nelson’s attempts to document the police ambush.

The book shouldn’t be mistaken for history, however: Some of Nelson’s sources have attempted to retract the unguarded statements they made under the assumption Nelson was writing a straightforward success story, and others are simply not talking.

One who did, though, is Tommy Tarrants, who in prison underwent an apparently sincere religious conversion and sat for more than a dozen interviews with Nelson.

Tarrants told Nelson at one point that the police would never have caught him had he continued to operate alone, as he initially intended . . . which means that Kathy Ainsworth is indeed an angel, if only to some degree and inadvertently, for having helped bring Tarrants to justice.