Apart from his insistence on training his light on corruption, thereby satisfying the public's right to know what makes the muckraker tick? It's a question to which Jessica Mitford latest book, a collection of 17 articles covering a 22-year span in Mitford's development. Tidied up, they are offered with revisions based on the original manuscripts-revisions which offer a glimpse of how magazine editors maltreated her work as a result of their crotchets and timidities.

To be sure, Mitford also has her crotchets, but "timid" is probably the last pejorative her enemies will ever tag her with. In fact she is an older, more even-tempered, better read Jane Fonda who has maintained her activism long past middle age and carried on energetically in the fact of increasing disillusion. What energy, not to say melodramatic vehemence, is packed into her observation that successful muckraking demands "an appetite for tracking and destroying the enemy."

Mitforrd hates pomp and her prose is unpretentious. She writes no odes to the Establishment and has confessed in her earlier book, "Daughters and Rebels," that as a young girl she used her diamond ring to scratch hammers and sickles on the windows of the family mansion. Her parents, Lord and Lady Redesdale, met Hitler in the '30s and became enamored of fascism. Although the germs of facsism attacked the Redesdale children, they failed to infect Jessica. She finally signaled her contrariness by eloping with a nephew of Winston Churchill who believed communism was the royal road to utopia.

The youthful couple's own road was filled with dangerous stretches. Jessica's husband fought and died in World War II. She crept above the poverty line through the mercies of a federal job in Washington and eventually married a D.C. lawyer. They moved to California, where she dropped the Communist party without taking the routine, self-abasing turn to the right.

Mitford's liberal political bent has an unmistakable English slant and in her first important magazine piece, "Trial by Headline," included here, she made her plea for finitude-in this instance, strict boundaries to the First Amendment. Her article told of an alleged rapist who was turned into a waxworks monster by San Francisco papers and described as the "fang fiend" even though observation would have shown reporters that he had normal teeth instead of overhanging ones comparable to tusks.

Her energy and "appetite for tracking the enemy" took her to Egypt in 1977 where she collected material for "Egyptomania," an article on archeologists whose diamond-hard professionalism had reduced itself to "malicious joy in the misfortune of others.' A more rewarding trip to the Deep South in 1961 introduced her to the drawing-room ladies she immortalized in "You-All and Non-You-All." Their lisps and Victorian fastidiousness concealed an adaptability to change. Said one: "I want you to meet my li'lole jailbird daughter. She's just been in and out of those jails since the sit-ins started . . . and now she's on her way to Jackson with the Freedom Riders."

"A Talk With George Jackson" offers a grimmer look at racism. Coming away from San Quentin, Mitford was haunted by Jackson's prediction that he would be murdered by a prison guard.

Whether she agreed with Jackson that the "criminals are in the Social Register" is problematic, but she was without doubt impressed by his integrity as she was depressed by his betters' lack of it. The betters play a sorry role in "Let Us Now Appraise Famous Writers," an attack on a correspondence school and the celebrated authors who endorsed it. This fascinating article, a brilliant illustration of her "investigative techniques," helped shut down the school and satisfied her that she had achieved "one of the few clear-cut successes . . . of my muckraking career."

Under the head of "Comment," Mitford introduces fresh material covering her motives and methods. In contrast to her subject matter, her range of ideas is narrow, but she is a witty writer with a gift for ingratiating rather than malicious irony, her workmanship grew increasingly resourceful under the space limitations imposed by magazine editors, and her many pages of advice to apprentice authors on how-to and how-not-to make a useful contribution to the craft.