Jack Klugman has found no difficulty in making the switch from Oscar Madison in "The Odd Couple" to the role of a medical examiner in NBC's "Quincy."

Sitting in his trailer outside Stage 25 on the Universal lot, Klugman said: "This is what I did orginally. Before I did "The Odd Couple," they said, 'He can't do comedy.' Then you do comedy and they say, 'He only does comedy.' So then you realize you're doing it for yourself. You say, 'You want me, fine. You don't want me, fine.'

"I don't live high off the hog and I can tell them all to go bug off. You don't know what it means for a Jewish boy to be able to say to a boss, 'Shove it.' It's such a joy.

"I have always been frightened of big business. It's always scared me, I used to go into an office of a boss and think about the respect I owe this man. I don't do that anymore.'

Klugman can afford that attitude. "Quincy," which was inserted into the NBC schedule last fall as a 90-minute show on the "NBC Sunday Mystery Movie" and later moved to its own hour slot on Friday nights, is attracting a faithful following.

Much of this stems from the passion Klugman brings to his role and to the subjects the show deals with. A few weeks back it was child abuse. On Friday, the subject will be rape.

When the original script for "Quincy" was sent to him, Klugman had his doubts about doing it. But in the past few months, Klugman feels that Universal "has let me have my head.

"I told them that I didn't want to do mystery shows. I didn't want to do 'McCloud' - not that I don't like that show. It's just not my kind of show. I wanted to do something that had something to say.

"I came into the theater with Clifford Odets, with the Federal Theater Project. That's what I saw, that's what influenced me. I saw 'Golden Boy when I was 14. John Garfield, who starred in the stage play, was our big hero.

"He was a big star in our neighborhood in Philadephia. Just from seeing him in coming attractions, everyone was quoting the speech he made as Mickey Borden sitting at the piano in 'Four Daughters': 'Sure, sure, they give you just enough talent. You can't play great. They're going to kill you. It was a beautiful speech. And it was what it was what all of us were thinking. We don't get a break."

Klugman, who is fascinated by politics, dwelt on the '30s a great deal as he explained what he was trying to do in "Quincy." "Most of us who came out of that era shared the view that socialism - mild socialism - would be the answer, that an Upton Sinclair kind of socialism would save the world.

"What Sinclair did with his exposes is what I want to do with this show. I want to expose things, situations that can be corrected with legislation. And yet, I also want the show to be entertaining."

Klugman conceded that such shows can often fail and Universal has had experience with them. "The front office is scared of it and they're right. They say, 'Listen, we did shows like 'The Senator.' That was a terrific show and bombed. So they have a point.

"It's just that I don't want to do shows where the dialogue is 'Move over here, move over there, put up your hands, these are your rights."

Klugman said he recognized that there was a fine line between drama and preaching. 'It's been my whole way of life.

"Preachments are acceptable by evangelists, if they are good speakers and believe in what they saying. The people who go to see Billy Graham are entertained. They are not bored with it because they believe in what he is saying."

Suddenly, Klugman remembered that it was time for the Norton - Bobick fight on television. And faster than you could say Felix Under, Dr. Quincy, Medical Examiner, with the Racing Form lying on top of the televisionset, was Oscar Madison again. For the moment, Upton Sinclair was taking a back seat to Ring Lardner.