Their sibling-rivalry humor is only slight exaggeration of life. Smothers Brothers' 20-year show

``Our life is a long-running series,'' says Dick Smothers, trying to define himself and his brother, Tommy, over a platter of clams. The three of us are lunching in the dining room of the chic Regency Hotel on New York's Park Avenue, where they have chosen to stay on the eve of their CBS-TV special tomorrow, ``The Smothers Brothers 20th anniversary Reunion Show.'' This is not a tourist hotel, and sports-jacketed Dick is proving to be the only tieless diner in a restaurant filled with seriously suited people.

``We've been basically the same act all our life,'' Tommy chimes in. He interrupts Dick all the time. And vice versa. It's impossible to conduct a two-way conversation with either of them; they compete for attention with each other, break into each other's remarks, quarrel good-naturedly, and make up constantly, just as they do in their sibling-rivalry act. Throughout it all, there is a feeling of brotherly love and undertanding.

``There's these two brothers,'' says Dick, ``and they sing and work together 30 years in show business. They don't change that act. They just get better at it. We can't change the premise, because we are two brothers. We're a classic. We can never get lost, because it's not an act, just an extension of our basic personalities, exaggerated a little.''

Tommy picks it up without missing a beat. ``The first 10 years, it was me working hard. Now, in the second 20 years, it's got more texture. Dickie is an exceptional straight man. The quality comic teams of the past all had exceptional straight men - Laurel and Hardy, Abbott and Costello, Martin and Lewis. The straight men never begged for laughs - they were very straight.''

Dick: ``Once I tried to be the comic, just for fun, and I didn't get any laughs. Look at the recent movie `Ishtar,' with Warren Beatty and Dustin Hoffman. It didn't turn out right, even though they are two brilliant actors. There wasn't a straight man. Neither of them was believably stupid enough. We could have done it so much better - and so much cheaper.''

Tommy: ``That's a great idea. Let's do a remake. A remake of a bomb!''

The talk turns to the time 20 years ago when CBS fired the Smothers brothers because they couldn't be prevented from airing relevant material. If they had a weekly variety series again, would it be political?

``We weren't political,'' Tommy objects. ``We were politicized by the times. We put on social observations, morality judgments basically. But all the people who performed were entertainers. Some with strong points of view, of course, but basically entertainers. We were never part of any political group.

``We tried to reflect what was wrong with the times - Vietnam, for instance. But we didn't think of ourselves as political. This reunion show has a very strong non-verbal attitude by all the people, a social point of view. If we had a series now, we'd do it the same way.

``But things today are not as black-and-white as they were then. And we're 20 years older and maybe a bit more mature. However, if we tried to do apartheid and Nicaragua stuff now, they'd pull us off again. You don't hear anything about those issues in prime-time entertainment today.

``Look, we were in the middle of a revolution. George Harrison once told us that it didn't matter if we were there or not; it would have happened. But it was nice to be in the middle of it.''

Could the Smothers brothers be in the middle of the battle for change in the 1990s?

``No. Someone else will have to do it,'' says Tommy.

``You can't fake an attitude,'' explains Dick. ``Anyway, in the old days we were making a stand more against censorship by CBS than anything else. Somebody stepped on our toe, and we said get off our foot.''

CBS, after they fired the Smothers brothers, lost a court battle and were forced to pay them a large sum in 1974. Since 1969, the brothers have been performing regularly on the nightclub and one-night-stand circuit. Not too many concerts at colleges, they say, where the youngsters are not as familiar with them as were their parents.

What would have happened to the Smothers brothers if CBS had not taken them off the air in 1969?

``We would have stopped that year as performers anyway,'' says Tommy. ``And, with the team of writers and other talented people, we would have become a production entity like the Norman Lear organization. I would be producing.''

``He'd be supporting me,'' says Dickie.

How would the brothers define their personality differences? Tommy is 22 months older and insists that, in the long run, he must always be protective of his kid brother.

Dick: ``I am a pragmatic, logical person. I was a math major.''

Tom: ``I'm moved by emotion, not by logic. As a matter of fact, I used to tell Mom that if we were placed in a Cuisinart, we'd be one perfect person. By the way, although it was a part of the act, Mom never really did like Dickie best.''

They think TV variety shows haven't been done well for a long time.

Tommy: ``Dolly Parton has been badly used by having her on all the time. It was the case with Joan Rivers, too. They should be hosts mostly. I believe in the judicious use of talent of the presenter.''

Dick: ``It's like a jazz combo - the lead guy comes out and plays a few riffs, and everybody else is weaving the whole thing around him. That's what we did in the old classic show.

``They're making Dolly do everything, playing solos throughout the whole set. I haven't seen anybody do variety right for 15 years.''

What would the brothers like to do in the future as performers?

Tommy: ``Live performance around the country, a regular platform on television, a movie - across the board. After all, we are the ultimate entertainers - we sing, do comedy, introduce guests well. But more than anything else we'd like to do a one-man, two-brother Broadway show.''

Are the the Smothers brothers preparing a Broadway show now?

Dick: ``We've been preparing for that show for the past 20 years.''