------------------------------------ SUNDAY NIGHTS AT SEVEN The Jack Benny Story by Jack Benny with Joan Benny Warner, $19.95, 302 pages ------------------------------------ The late Jack Benny wrote an autobiography that was known to almost no one. So few, in fact, that his only daughter Joan was surprised to find the finished manuscript among her mother's files after her death in 1983. Joan Benny has augmented her father's words with her own memories and some interviews accomplished expressly for the book. It is very good.

As one might expect from the most popular comedian of the age of radio, Jack Benny's memoirs are fast-paced, lively, and entertaining. His recollections are positive, and he says almost nothing negative about anyone.He traces back to his humble beginnings as Benjamin Kubelsky in Waukegan, Ill., and reveals many intriguing facts about his early life and entry into show business.

He was a high school dropout (although, as he notes with irony, Waukegan eventually built a junior high school in his honor) and took to serious study of the violin only after flunking out of the family haberdashery business. (Do we have to know their names? he asked his father after an unknown customer left an account payment with him.) Over his mother's objections, he eventually found employment as a violinist with a local touring singer. After a while, he began to talk, which grew into a comedy monologue.

Jan Kubelik, a concert violinist, forced Benny Kubelsky to change his name in 1912. He next became Ben Benny, and became fairly well known as a violin-and-comedy performer.After serving in the Navy in World War I, a similar entertainer named Ben Bernie forced him to change his name again, and he chose the name Jack, by which all sailors in the war were informally known to each other. Some of the stories have been told before, but get a much- deserved retelling from the horse's mouth here. Jack met his wife, Sadie Marks (she later changed her name to Mary Livingstone, the name of the character she played on the radio show) when he was 27 and she 14 at her family's Passover celebration in Vancouver.

She was related to the Marx brothers, and Zeppo Marx (then Marks) had brought his colleague to the home for the occasion. Mary insisted that Jack listen to her violin playing.He found it horrible and he and Zeppo made a quick exit. Several years later, they met again and married in 1927 after a brief courtship. It was only after they were married that Mary reminded Jack of their first meeting. Jack continued his successful career in vaudeville, and when his partner took ill, he persuaded Mary to fill in.

She was a hit. Eventually he found himself on Broadway and then in the movies. He vacillated for a time before deciding that going into radio would be worthwhile.While they were living in New York, they adopted Joan.

She learned in writing the book that Mary Benny had planned to take her only to nurse her to health while they awaited an arranged baby. (Jack opposed this idea.) Naturally, they found they couldn't part with Joan. Much of the book consists of Joan's writing. She seems to be in a different book from her father.

It would be a major help if she used a writing style that conformed more closely to that set by her father in the early chapters. Her short, simple sentences slow the pace in a sudden manner. She provides extreme levels of detail about her early life, homes, and the trappings of being a celebrity daughter. While this matter is interesting to a Benny buff, one hopes that none of the venerable comedian's material was subjugated to make room for it. It would be far more relevant if Joan Benny were a celebrity in her own right.

But this is the fall of 1990 and such things are to be expected of celebrity offspring. George Bush is our president and no doubt he approves. Some of Joan Benny's passages are curious. Obviously, had her father wanted details of his premarital womanizing in his book, he would have put them there himself. Her life is very well detailed up to about 1965, but she says almost nothing of her activities for the past quarter century.

Joan Benny pulls no punches in discussing her mother. The two had what would mildly be described as an adversarial relationship. Mary Livingstone Benny (who always introduced herself as Mrs. Jack Benny) is portrayed as a vain, insecure spendthrift.

She allegedly was most interested in being with and accepted by the Hollywood elite. Studio moguls, that is, not the entertainers that her husband called friends.Jack Benny attended Friar's dinners and the like alone. Mary Livingstone Benny may have played the role of Mrs.

Jack Benny to the hilt to gain social standing, but Joan Benny's words must be taken with a teaspoon of salt (or a more healthful sodium-free substitute) in light of the obvious delight she displays on every page at being Jack Benny's daughter. Jack Benny tells a good many anecdotes that have not been printed before. Obviously, none of the three Benny intimates who wrote biographies had access to this material.He tells how he learned from others' mistakes in developing his radio style. (Other comics used visual material for their studio audience, which left home listeners in the dark about what was so funny.) There is a certain paradox in the greatest radio comedian also being the greatest user of facial expressions and body language.

Perhaps, as Jack suggests, his secret wasn't those mannerisms but his timing. Jack acknowledges that he was but a mediocre violinist. Nevertheless, he won the respect of some of the world's greatest violinists. These stories are a treasure.Isaac Stern called him the most fortunate concert artist because he didn't have to live with the pressure of having to be perfect.

The book is must reading, but the reader can't help but agonize over how much better it would be had Joan Benny published the autobiography verbatim (Jack wanted to title it I Always Had Shoes, a reaction to comedians who claimed to have risen from abject poverty) or more successfully integrated her words into it. With any luck, the book will spark a renewed interest in the legendary comedian. His television show could stand to be revived by one of the cable networks, and a TV movie about him is a possibility. Joan Benny selected dozens of family photos for the book; they are a contribution.

The most striking thing about the book is how fresh Jack Benny's words sound, even though they were written almost twenty years ago.It's almost like having him back.