GOLLY, GEE whiz - who would have thunk it?

Beaver Cleaver selling insurance in California . . . Jeff Miller (Lassie's best friend) busted for cocaine smuggling . . . Dennis the Menace swabbing decks?

"I joined the Navy a year ago," said Jay North from the quarterdeck of the U.S.S. Iwo Jima, docked in Norfolk, Va., last week. "I decided to get away from show business. I needed a break."

North, who played TV's Dennis (the Menace) Mitchell from 1959 to 1963, left Hollywood for a stint as a seaman's apprentice. "My day consists of hard work on the ship," he says. "My shipmates know who I am. There's a lot of good-natured kidding."

Jay North is 26 years old, stands 5 feet 11 and weighs 155 pounds. The platinum hair is dark blond now. The cowlick is gone.

But one thing that hasn't changed is the voice - still squeaky clean and slightly naive. You almost expect to hear "Jeepers, Mr. Wilson" or some other goofy line from the family comedy, (based on Hank Ketchum's comic strip) currently rerunning on weekday mornings.

"I don't really remember much about the show," he says matter-of-factly. "So much has happened since then. It was just a job."

North's career as a child actor began at the age of 5 with an appearance on a local program in his hometown - Hollywood. His mother, Dorothy North, worked in the local AFTRA office, and says, "I didn't push him. He was the one who wanted to be on television."

North landed a part on "77 Sunset Strip" and made a few commercials before Screen Gems signed him as "Dennis the Menace" in 1959. "I was seven years old," North remembers, "Growing up in show business is a tough way to live."

Gloria Henry, who played Alice Mitchell (Dennis's mom) says, "He was a beautiful little boy, a good little boy, but a bit cushioned from reality. It's a shame he was robbed of his childhood."

Jay was accompanied on the set by an aunt and uncle while Mrs. North worked. "They were so proud of how grown-up Jay was," Gloria Henry remembers, "relating to directors and people on the set. But he felt the pressure nevertheless."

Mrs. North, who now works in a health food store in Hollywood, says she feels that "he had a much richer life because of it, much broader horizons than other children his age."

After "Dennis the Menace" went off the air, North appeared in two feature films, "Zebra in the Kitchen" and "Maya," which became a television series in 1967. It lasted one season. Then he tried dinner theaters, a few voice-overs, but nothing seemed to click.

"I made some money from the show," North says. "But it's all invested I can't touch it."

Married in 1973, he and his wife were divorced a year later. "No children," the child-star says, "and I never really went in for dating starlets. I don't dig that scene. And I don't do drugs either. I decided I didn't want to be part of it. I guess you could say I'm the all-American boy."

Not like Tommy Rettig, who played Jeff Miller on the television series "Lassie." Rettig was arrested several times on drug charges until three years ago when he was sentenced to a 5 1/2-year prison term for cocaine smuggling. The case is still under appeal, and Rettig is free on bond in California.

"I knew Tommy," says North. "And I knew John Provost who replaced him on Lassie. And Jerry Mathers, of course." Mathers ("Hi Mom, Hi Pop, Hi Wally") is now selling insurance in California. Contrary to counterculture rumors, "The Beav" was not killed in Vietnam.

"I've tried to keep up with them," says North, "But the business has changed. It's not a fun as it used to be." Especially for child stars who - at the age of 13 - may be all washed up.

"That's exactly what happened to Jay," says Gloria Henry, who has kept in touch with her surrogate son. "After all, he was a star. All of a sudden there no parts of him. I think he's quite bitter."

Henry said she and Herbert Anderson, who played Dennis's father, wanted Jay to quit show-biz and get a good education. "Billy Booth, who played Tommy on the show, went to law school. Now he's a very successful lawyer in Los Angeles," says Henry. "Jay's mother wanted him to stay in show business. He did everything to please. But I don't think he really knew what it meant to be a child. He should have gone to school."

His mother puts it this way, "This Dennis the Menace image was difficult for Jay to get away from. He was type-cast. It's a shame, because he is one heck of a good actor."

As for North's attempts to shake the little devil image, "I grew into a totally different person," he says. "I'd have to start all over again. And now, my only commitment is to the Navy, though to tell you the truth, I'm not that crazy about it. In fact, I'm disappointed. I have three more years to go and after I get out, I suppose I'll hve have to make a decision whether or not to return to show business."

Dorothy North thinks her son "probably" will. Gloria Henry says she always thought he wanted to go into law enforcement. As for Jay North - well, as he put it, "I've never done anything in my life I wanted to do."