Jack Klugman is turning in his scalpel and his microscope to "watch his horses beget." But even if he leaves "Quincy," as he announced this weekend, there will always be a lot of the doctor in the actor.

Now 58, Klugman is invited to speak to medical students, and lends his celebrity, as he did before a congressional committee just two weeks ago, to medical causes such as the hearings on so-called "orphan" drugs. And, he says, he felt pretty good about it when he spoke before the graduating class at Mount Sinai Hospital last year "until I realized that not one acting group has ever asked me to speak."

"I thought to myself, "Who the hell do they get . . . doctors?'"

All that changed Saturday night, though, when Klugman-Quincy co-emceed the Ford Theatre gala.

Well maybe it didn't change all that much. There he was musing about what Dr. Quincy would have done about the Lincoln assassination. "I [notice the first person] would prove," he said, "that Booth didn't do it at all, that it really was an usher." Then, warming to the subject: "You see, Lincoln hadn't tipped him in two years, and he got revenge. Booth happened to be going by, heard the shots, jumped and everybody thought he did it . . ."

Saturday morning he was sitting in his Madison Hotel suite hoping the snow squall would turn into something, and inveighing against a murderous schedule that would take him from rehearsal to White House to performance to reception with no time to shave again and only a dubious promise of food.

He announced cheerfully that his lawyer had found an alleged "breach of contract" on the part of "Quincy" producers and, on that basis, Klugman tendered his resignation Friday as TVs feisty forensic.

He'd like to tour four months a year in theater productions and breed horses the rest of the time on 20 newly purchased prime acres in California, he said, although he concedes that there may be some legalities to overcome before he can actually quit the show.

In town with his lady of some six years, Barbara Neugass (featured with him, to their disgust on this week's cover of the National Enquirer), Klugman teased that she's one-third of the tabloid magazine's "Klugman triangle."

"They do hatchet jobs about me all the time," he sighed. "You can't believe this kind of arrogance . . . and they're finally getting their comeuppance."

"Thank God," echoed Neugass, "for Carol Burnett."

Lean and fit in a green wool sweater over a blue shirt -- his eyes looking one color at one moment and the other color the next -- Klugman says his health is fine. "Oh," he said, "I had a little trouble with my throat, but it was nothing . . ."

It is snowing outside, not in, but he wears his trademark Irish walking hat, or tennis hat, custom-made from a soft tan corduroy. Yes, he wears a hat all the time. (The white one is for luck, put in Neugass. It is the superstition of the true horseman.)

Explained Klugman, "I get them made firstly, because I'm bald. Secondly, my mother always said keep the top of your head covered and you'll never catch a cold." (So much for Quincy.)

Klugman is unabashedly proud of "Quincy" scripts on such things as parent abuse, rape, orphan drugs, which he calls "relevant" but which he says early "Quincy" producers called his "relevant crap."

He was brought up during the Depression in the South Philadelphia neighborhood that also produced Joey Bishop, Fabian and Mario Lanza -- a schoolmate. And, as he quickly will tell you, he was nurtured on the traditions of Clifford Odets, Maxwell Anderson, Upton Sinclair.

The trouble was, by the time he was successful enough to make some sort of social contribution, socially conscious theater had gone the way of bread lines. After five seasons as Oscar Madison on "The Odd Couple," Klugman felt he had finally found his forum with "Quincy" -- part doctor, part cop.

"I had to convince them that when you said relevance you weren't saying poorhouse. And I said, 'Believe me, there is money in relevance . . . you'll make a profit. Just look at "60 minutes"' . . ."

He sounds just like Quincy. "Oh sure," he said, "I guess I'll miss it."

"But it's been six seasons. It's time to move on."

And on his role-modeling for midlife men? He gives a great Quincy-like sigh.

"I'll tell you how terrible it is to become a sex symbol in the twilight of your life," he said, not sounding as though he thought it was terrible at all. Then he repeated, "A terrible thing. Where the hell was it when I needed it?"