The license plate on her brown Ford Monarch reads JAN WHO. A more appropriate label would be "Survivor."

Actress Jan Clayton, who went from B films to Broadway, is probably best remembered as Tommy Rettig's TV mom on the '50s Lassie series. Along with a fluctuating career, Clayton weathered three divorces, the death of her eldest daughter in a 1956 auto accident and a 10-year bout with alcoholism.

"My drinking got worse after my daughter died," says Jan. "Before that I was a social drinker. But even then after a few drinks I'd get the sillies, then the cries and finally the meanies."

Clayton, 59, has been on the wagon for seven years. In 1970 she joined Alcoholics Anonymous and today counsels other alcoholics on how to reclaim their lives. Every Thursday she answers the phone at the Alcoholism Council of Greater Los Angeles, where she recently was made a board member. "I usually get about 25 calls for help," Jan says. She is also on the advisory board of the Detoxification Rehabilitation Center, known jokingly as the "Skid Row Group." For them, Clayton says, she begs money shamelessly. "Socks and shoes, that's what they really need."

Born in Alamogordo, N.Mex., the only child of two schoolteachers, Clayton started singing at 4. She went to Hollywood in 1937 after winning a talent contest, appeared in a few horse operas and met her first husband, cowboy actor Russell Hayden. Their late daughter was named Sandra.

In 1945 the producers of the musical Carousel picked Jan for the starring role of Julie. She was such a hit that when Oscar Hammerstein II and Jerome Kern were casting Show Boat they offered MGM their future services for $1 if the studio executives would allow Jan to play Magnolia. While in Show Boat, Clayton met Robert Lerner, an heir to the women's clothing shops bearing his name. They were married and moved to California, where Lerner attended Loyola Law School and Clayton concentrated on mothering. "We had three children in three years. Then came Lassie. I took it because I was dying to work."

After four years of shooting six days a week, she quit. "My home life was being absolutely wrecked," she says. "I had four children and a husband, and I was always working." The marriage failed anyway.

But, as in every installment of Lassie, all has turned out well. Clayton lives with two cats (one named Tommy the Rettig) in a three-bedroom cottage with a swimming pool. Still close to Rettig, now 33, she testified for him recently in a drug case. Her daughter Robin, 28, a department store buyer, and son Joseph, 26, a sci-fi writer, come by to do their laundry and chat. Another daughter, Karen, 27, lives in Mexico.

A year and a half ago Clayton began helping an old friend, Sam Marx, research a book about Richard Rodgers and Lorenz Hart. And now "Jan Who" is a writer. Bewitched, Bothered and Bedeviled will be published in October, and Clayton shares the author's billing.