It's hard to know how to classify Steve Allen.

Author (with 35 books to his credit, including two recently published detective novels with himself as the hero). Actor (the title role in "The Benny Goodman Story" among others). Comedian ("The Steve Allen Comedy Hour" etc.). Composer (the Broadway musical "Sophie" and thousands of songs). Creator and first host of the "Tonight" show. And that only scratches the surface.This weekend, however, he takes on a new role, at least locally, as soloist and guest performer with the Utah Symphony on its annual retirement-fund benefit concert Saturday, Oct. 20, at 8 p.m. in Symphony Hall.

Even then I expect he'll be hard to classify.

I still remember him best as the host of "The Steve Allen Show," which between 1956 and 1960 provided a forum for not only his own off-the-wall antics and improvisations but also the most astonishing array of new comedians ever to grace the airwaves. (And no, I haven't forgotten the various incarnations of "Saturday Night Live.")

Don Knotts, Louis Nye ("Hi-ho, Stevarino"), Tom Poston, Bill Dana, Don Adams, Lenny Bruce, Tim Conway, Mort Sahl, Shelley Berman, Jonathan Winters, the Smothers Brothers - all received their first big network-TV exposure via Allen, as did such non-comic types as Elvis Presley (yes, even before Ed Sullivan), Lou Rawls, Miriam Makeba and Jerry Lee Lewis. (The last was so grateful he named his son after Allen.) One show I remember offered us Anthony Perkins, singing "Moonlight Swim." Another featured Orson Welles in excerpts from "Othello."

Singers Steve Lawrence, Eydie Gorme and Andy Williams were likewise Allen discoveries, appearing with him for many years on the "Tonight" show.

Still, I expect what Allen himself would most like to be remembered for is his Peabody and Emmy Award-winning PBS series "Meeting of Minds," which, with the help of actors, gathered the likes of Shakespeare, Socrates, Galileo, Marie Antoinette, Darwin, Emily Dickinson and Attila the Hun together for what usually turned out to be a lively round-table discussion.

That's certainly as close as he comes to admitting to being proud of anything he has done in his long and varied career.

"I think a thousand years from now those shows will still be seen," Allen says. "People won't have any interest in who the tall guy with the glasses is, but they'll still have some in Plato, Aristotle, Luther and Aquinas."

You never know. After all, the old "Steve Allen Show" also won a Peabody Award its last season. Currently the bespectacled entertainer is involved in editing those kinescopes into 100 half-hour episodes for broadcast over MTV's HA! cable comedy network beginning this month. He is also listed in the 1985 Guinness Book of World Records as the most prolific composer of modern times.

"But I didn't struggle for any of that," he says, maintaining that "I'm actually a musical illiterate, with a primary gift for composition and another for playing the piano. But it all came very easily."

Writing, Allen says, was the first gift to emerge, in the form of short stories and essays turned out around age 10 or 12.

"My high school English teacher encouraged me in that direction. `But,' she said, `that's a very demanding profession and I think you should stop acting in all the school plays, horsing around in assemblies and playing in the dance band.' Then my music teacher would give me the same advice, pointing me in the direction she thought my gifts suggested. Happily I was able to get into a field - at first radio, then television - that could accommodate all my abilities."

As for his ability to detect talent in others, Allen attributes that to his family's background in vaudeville. "Both my parents worked in vaudeville and I spent my early years in and around theaters. So I can smell talent at 1,000 yards and non-talent at 2,000."

At the same time, Allen maintains, "the American people really have very little interest in talent. What they're morbidly fascinated by is success."

To some extent he attributes his concert career to that. "I never would have thought of doing anything like that myself. But about 20 years ago Arthur Fiedler and the Boston Pops called and said, `We'd like you to conduct our orchestra.' I said, `I'm honored by the invitation, but I'm not competent to do that.' `That's OK,' they said. `Danny Kaye isn't competent either, and he does it.' I said, `No, that requires a real musician.'

"What I ended up doing was coming in the capacity of a pianist/composer and performing a concert of my own music. I used to include something I wrote in the classical mode, but now its mostly pop - melodies I've written over the years, some well-known and some that are not."

In the first category, Allen will be treating his Utah Symphony audience to such semi-standards as "Impossible" and "This Could Be the Start of Something Big" (which he claims came to him in a dream) as well as a song he says is "making something of a comeback," "Pretend You Don't See Her," featured in the new Martin Scorsese film "GoodFellas."

In addition music director Joseph Silverstein will lead the orchestra in a trio of Russian works, the Overture to Glinka's "Russlan and Ludmilla" and Tchaikovsky's "Andante Cantabile" (from the String Quartet No. 1) and "Capriccio Italien."

If all that sounds pretty straight, I wouldn't bet on it. At 68, Allen comes across pretty seriously on the telephone, but I can't remember many times when he sat down at the keyboard without making an ad-lib of some kind. This is the man, after all, who used to entertain late-night viewers with such top-of-the-head stuff as The Question Man ("He rode from Lexington to Concord shouting, `The British are coming! The British are coming,' " was the answer, to which Allen would provide the question "What did Harvey Hackensack do to get arrested for drunken driving last New Year's Eve?") and diving into 9 feet of Jell-O.

Allen says his own early influences ranged from Robert Benchley ("I don't see him so much in my work as in my writing") to Fred Allen (no relation) and Groucho Marx. As for the state of the entertainment business these days, he has mixed feelings.

"If you're talking about comedy," he says, "it's in very good health by certain criteria. Back in the '50s I wrote a piece for the Atlantic in which I made the casual observation that there were only about 15 comedians in show business, a number so small you could fit them all in a school bus. Today we have over 2,000. We're also the first generation in human history that has been brainwashed by comedy, literally from birth as the hospitals have TV sets on the walls.

"But unfortunately not all the comedy to which we're exposed is admirable, particularly at present. It's frightening to think what it's going to be like in another 15 years, when today's 7-year-olds, having seen films in which they're exposed to a good deal of pornography, are grown and have to fill the roles of husbands and wives and parents. How well prepared will they be?"

"Meeting of Minds" was an effort to address that problem, Allen says, as was the book "Dumbth, and 81 Ways to Make Americans Smarter." Another attempt was the children's record "How To Think," which came out around 20 years ago.

In between, though, come the jazz and symphony dates and the comedy concerts (one of the latter coming up soon in San Antonio). Because when you think about it, in a troubled world the ability to generate laughter isn't such a bad thing to have either.

Tickets to Saturday's concert range in price from $10 to $23, with proceeds going to the musicians retirement fund. For information call the Symphony Hall box office at 533-NOTE.