At a time when newspaper comic strips have become hastily drawn repositories for bad puns and cornball jokes, it's something of a shock to come across Calvin and Hobbes. What are wit, sarcasm and grace doing on the funny pages?

Calvin is an ordinary kid, part devil, part heartbreaker, roughly 6 years old. He's the sort of child who, confronted by a substitute teacher at school, demands to see her teaching certificate.

Hobbes is Calvin's little stuffed tiger, who, when there aren't any adults around, turns into a large, dreamily philosophical, real tiger.

Surrounded on the comics pages by trendy yuppies and smart-mouth kitty- cats, Calvin and Hobbes is an oasis of surprise and subtlety. The 18-month- old strip, syndicated in 250 newspapers, is also the hottest comic in newspapers today. The first paperback collection of Calvin and Hobbes strips, just published by Andrews, McMeel & Parker, is already on the best-seller lists of the B. Dalton and Waldenbooks retail chains.

All this leaves the strip's creator, 28-year-old Bill Watterson, groping for an explanation.

"It's unbelievable," said Watterson from his home in Hudson, Ohio, midway between Akron and Cleveland, where he lives with his wife, Melissa, a painter. ''Right now, I just keep thinking how lucky I am. I'm doing what I've wanted to do since I was a kid, and people apparently like what I've created."

To Watterson's commercial success, add critical acclaim as well. Calvin and Hobbes is "the freshest strip to come along in 10 or 15 years," Richard Marschall, comic-strip historian and editor of the monthly comics magazine Nemo, said last week. "Offering us a kid's world through a kid's eyes is very hard to pull off, but Calvin is completely believable."

And Doonesbury creator Garry Trudeau, the least likely cartoonist to write a book blurb, wrote a glowing foreword to the Calvin and Hobbes book. It is Watterson's gift, says the father of three, to capture "childhood as it actually is."

For his part, Watterson claims not to have the foggiest idea what children are "really like." "I don't have kids, and I know that Calvin does some things that a 6-year-old probably doesn't do - I often have him writing long book reports in school, for example. Six is just an approximate age. Basically, Calvin does what I'd like him to do, and a little of what I remember doing - or wishing I could do - when I was a kid."

The soft-spoken, articulate artist has firm ideas about comic strips, their creators and the business that surrounds them. "I don't think comic strips are children's entertainment. You can talk about subjects with sensitivity and intelligence in comics," he said. "Most strips emphasize the joke, the gag. I hope I'm doing more than that. Without wanting to sound pretentious or anything, I'm trying to make readers laugh and deepen their understanding of the characters a little bit more each day."

The road to overnight success was a tedious journey for Watterson. "To establish a comic strip, you have to send out drawings and ideas to the various syndicates. I was doing that for about three years while working in the art department of a little weekly tabloid shopper," he said. One of the comic-strip ideas he pitched was a Star Wars parody called "Spaceman Spiff."

"It was so bad," says Watterson now, "that I make fun of it in Calvin," and indeed, there is an occasional strip in which the daydreaming boy imagines himself the brave but bumbling Spiff.

Watterson landed a job as the editorial cartoonist for the Cincinnati Post. Since he had majored in political science at Ohio's Kenyon College, he figured he could handle the assignment, but he didn't make it past the six-month trial period. "The paper wanted a lot of local commentary, and I'd never lived there before. By the time I was getting the hang of the byzantine local political situation, I was history."

Calvin and Hobbes (the names are snitched from Protestant reformer John Calvin and philosopher Thomas Hobbes - "an inside joke for poly-sci majors") was an idea Watterson had had for a long time, "but I never thought any syndicate would go for the Hobbes-as-stuffed-toy-and-real-tiger idea. As it turned out, the first place I showed it to was wild about it. It just goes to show, never underestimate your readers."

The emphasis on young Calvin's imaginary life gives Watterson a creative freedom many of his colleagues don't possess. "The strip has another dimension and opens up all sorts of possibilities. If I want to do a comic strip about an octopus for a couple of days, for example, I just turn Calvin into an octopus."

Watterson recently broke with the usual humorous, anarchic tone of his work by spending a week's worth of strips exploring Calvin's shocked, saddened reaction to discovering a dead raccoon in the woods near his house. "It was a risk," he said. "I got quite a few letters from people who had lost relatives recently and said they appreciated the strips. It surprised me that a fictitious cartoon death would move people, but it's wonderful that it has.

"Part of the challenge in those strips in particular but also in comics about kids in general is avoiding the temptation to blast the subject with schmaltz. There's a cheap way to manipulate people with comic strips by drawing in a very sentimental manner - big, sensitive eyes, stuff like that - but I try not to do that."

Ask Watterson about his major influences and he quickly says "Peanuts and Pogo. Both those strips are phenomenal in terms of the depth and integrity of the characters and the quality of the writing. They both pushed the boundaries of the medium way out there. Of the more recent ones, I like Bloom County and Doonesbury."

Ask Watterson what comic strips he hates and his answer is even quicker. ''Almost everything else. Most of them are like Saturday-morning TV animation - complete garbage."

Nonetheless, the idea of seeing Calvin and Hobbes cartoons on television appeals to him. "Animation seems to be one of the few areas where I could communicate what I'm trying to get across on the printed page," he said. ''But it's not too likely anyone will see Calvin cartoons in the near future. I'd want to have so much creative control, and make the quality of the animation so much better than what's on TV now, that they'd probably be too expensive to make."

When a comic strip becomes a hit, its creator is inundated with offers to ''merchandise" his creation - just think of all the Snoopy greeting cards and T-shirts you've seen. "I've gotten a lot of offers like that, and I'm trying to sort out my feelings on this. I think you have to be very careful to maintain the integrity of your strip, because you can cheapen your work. It's very important for me that the comic remain a personal creation. I don't want some big corporation in New York or Los Angeles making decisions about creating greeting cards or something like that. I don't want to cave in to audience demand or the financial incentive."

What Watterson would like most, in fact, is simply to be left alone. "What I like best is drawing Calvin and Hobbes - I'm not good at social interaction." Watterson has refused to embark on the standard promotional tour to plug his book around the country.

"The publisher started out asking me to do three weeks in 15 cities. I said it would be no weeks in no cities. I hate the publicity aspects of this job. It keeps me from my work and I'm completely drained after every time I have to meet somebody or discuss my work. My brain would turn to guacamole if I went on a book tour.

"I think for my mental health and the health of Calvin and Hobbes I have to lead a normal life and not be concerned with the commercial aspects of the strip. My wife and I live in a small town, and it's nice to be able to walk around and not have to deal with autographs and stuff like that.

"Calvin and Hobbes is really fulfilling work. I don't need to be a star. Just being able to let Calvin run wild is enough of a reward."