'SNEAK PREVIEWS'

Gene Siskel sits in a soundproof room waving a grilled cheese and tomato sandwich and describing his professional relationship with Roger Ebert, a rival film critic and his ''Sneak Previews'' partner. ''I can look him in the eye and lie right to his face (on a story). He knows it. That's the way it should be. The public deserves that.''

Later, Roger Ebert is sitting in a room with Gene, their producer, and an assistant or two. He is stabbing at some three-bean salad and describing his relationship with Mr. Siskel. ''I'll tell you this much, I respect Gene a lot more since I've been working with him, because I can see his standards in operation.''

There you have it: two of America's best-known film critics critiquing each other for better or worse, for richer or poorer. Except in this case it's definitely for richer.

In the short span of five years, two Chicago newspapermen have found wealth, fame, and success in front of a TV camera. All this just for saying ''yea'' or ''nay'' to a bunch of movies? Move over, Vincent Canby and Pauline Kael, Roger Ebert and Gene Siskel have hit the big time.

Despite their success in the front-row balcony and their mutual love of movies, one suspects that the two former co-hosts of PBS's ''Sneak Previews'' - they will be seen this fall in their new show, ''At the Movies'' - are perhaps unnaturally linked. New York's alternative paper, the Village Voice, described them as resembling ''two eels fighting underwater.'' Gene describes it as: ''You dump on the other guy, basically. You tell your editors how lousy the other guy is and how great you are. Well, we still do all that. But in addition, once a week we do get together and talk to each other in front of a camera.''

That is indeed the point: their weekly, verbal tug of war over characters, plot, and believability - and all in language that plays as well in Peoria as it does in New York City. No reviewerese here, no motifs or covert symbolism or historical allusions. No, just ''Neither one of us can recommend you see this movie,'' or ''We both think you should see this movie,'' or perhaps one ''yea'' and one ''nay.''

Simple, eh? And successful: Audience estimates for ''Sneak Previews'' run to 6 million household per week. It has been the most popular half-hour show PBS has ever produced. Not for nothing are Ebert and Siskel considered among the most powerful men in the American entertainment industry. Two ''yes'' votes from the dynamic duo for a recent release can make the hearts of Hollywood marketing men sing for months. A ''no'' vote can cost, and cost dearly.

In addition to their national show, each reviews movies on local television newscasts. They also write film reviews for rival Chicago newspapers: Gene works for the Tribune and Roger writes for the Sun-Times. And while they consider themselves primarily newspapermen, the American viewing public knows them as media stars on the rise. Their love of the limelight is thinly veiled.

''Television is the ideal medium, in a sense, because you're reviewing movies and you can show what you're talking about,'' says Roger, speaking traitorous words for a print journalist.

Gene is just as enthusiastic about their impact. ''Let's say we're reaching 10 or 15 million people (each week),'' he postulates. ''You just can't help but sell tickets.''

Roger chimes in with some hard-core proof. '' 'My Dinner with Andre' had opened in New York, played for six weeks, and the closing notices had been posted, when we did it on 'Sneak Previews' that Thursday. The next Friday business tripled and did better than the opening weekend in New York. And it set a house record in Chicago.'' Whew.

With that kind of impact, it didn't take commercial television long to see the light. The boys have been snapped up by a local commercial station, which will syndicate the show -nationally starting this fall. PBS's ''Sneak Previews'' will stay manfully on the air with two yet-to-be-named replacements. But not to worry: Roger and Gene will still be paid very well to smile and snarl at each other and a whole bunch of new movies.

In addition to handsome salaries and free lunches (a perquisite that thin Gene claims is of immense importance to not-so-thin Roger), Ebert and Siskel will be reunited with Spot, the Wonder Dog, on their new show. The spunky little canine used to introduce the ''Dogs of the Week'' - the two critics' choices for the week's worst films. For those of you who may have wondered why someone ordered Spot ''out, out,'' now it can be told.

Even before Roger and Gene had encountered contract problems with Chicago's public TV station WTTW which led to their departure, Spot had fallen into the company doghouse because of ''salary demands.'' There also circulated a nasty rumor involving cheese bits and Slim Jims, but it seems a side issue now. Nonetheless, Spot will rejoin Roger and Gene on the other side of the airwaves, while his public television replacement, Zeke (whom Gene called ''uncontrollable'' to his face), will remain with the new hosts.

But all this contract talk is perhaps beside the point. The real fun is watching the boys be boys by themselves. Or maybe not by themselves, because they do seem to relish an audience, any audience. If you think they are charming and wise and amusing on TV, they try to be even more so off-camera.

To hear them tell it, they behave the way they do because they consider themselves to be rival newspaper writers first and foremost. This is enough to fuel the fervor in each for his own talents. Each privately regards himself as the better writer or reporter or both. What they possess for each other in public is professional respect. But they are cagey about showing it. Their verbal exchanges are as well played as any chess game.

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* The Time: 1:30 p.m. Thursday, the usual taping day for ''Sneak Previews.'' An hour before taping.

The Scene: An appropriately up-scale exposed-brick editing room, outfitted with de rigueur oak table and two Royal 440 typewriters (less up-scale, but a nice newspapery touch).

The Participants: Ebert and Siskel, of course, and their youngish-looking producer, who refuses to admit which of the two she prefers. Roger is wearing a colorful lime green-and-blue plaid shirt, while Gene sports a bright pink sweater. One supposes these colors will look very good on TV; in this room they glow like neon.

Both are typing furiously - Gene with two fingers - pausing, and typing again. Neither looks up or at each other. It is the second-to-last show the two will perform for public television. The air is filled with a kind of sulky purposefulness.

Suddenly Roger stops typing and starts laughing. ''Listen to this,'' he commands, and starts to read from his script without any outside encouragement: ''And Franco Nero, you remember him. Well, he started out as Lancelot and now he just uses his feet a lot.'' Roger has cracked his ample self up with this line. Gene, on the other hand, looks up sourly.

''I'm not talking to you,'' says Roger. ''I'm just reading out loud.''

''That's not funny,'' says Gene with no trace of a smile.

''It's hilarious,'' counters Roger.

''No it's not,'' Gene continues, refusing to surrender the last word on this obviously moot point. Both start typing again.

A few minutes later Roger booms out again: ''Gene, I must have your votes for the summary. Do you want to hear mine?''

''No, I don't want to know.''

(Roger aside: ''His nickname is 'Mr. Genial.' '')

Type, type, type.

Of course, they are serious critics, too. Both decry the recent proliferation of horror movies featuring violence toward women. Both applaud the recent surge of ''independent,'' or non-Hollywood, type of film. Both criticize the increasing ''televisionization'' of movies which, Gene explains, encompasses ''everything from shooting the movie in close-up so that it can be easily seen on television, to shooting in a narrow emotional range that'll pass for television, to employing stars that have a high TV rating like Henry Winkler, Suzanne Somers, Morgan Fairchild.''

But it is the differences between the two that are more telling. Roger teaches a film class at the University of Chicago and is the ''father'' of two cats; Gene is married. Roger ''dates extremely attractive young women'' and goes to ''wonderful places for dinner.'' Or so he says. Roger got a PhD and a Pulitzer Prize and has written a screenplay, ''Beyond the Valley of the Dolls''; Gene went to Haight-Ashbury after college and also spent some time in the Army.

There are obvious physical differences as well: Roger is short and overweight and wears a sweater on camera; Gene is tall, slim, and balding, and is always dressed in a sport coat. Roger reminds you of the smart, fat guy who sat next to you in English class. He may not have been much socially, but he was pleasant and had all the answers. Gene is more difficult to assess. He grew up in a wealthy suburb north of Chicago and went to Yale, graduating as a philosophy major.

Not everyone in the country is enthusiastic about them, however. For one thing, some of their newspaper co-workers are apparently a tad jealous of their fame and fortune. But as Gene readily concedes, ''I would be, too.'' Other newspapers have taken unkindly swipes. Chicago's alternative paper, the Chicago Reader, has thrown its barbs at Gene, anyway. It ran a short-lived column called ''The SiskelWatch'' in which purportedly blatant film-reviewing mistakes made by Siskel were held up to public derision.

But none of these petty annoyances appear to mar the TV-smooth surface that each of the critics possesses, Yale degrees and PhDs notwithstanding. They seem to understand very well their secret to success.

Gene leaps right in with his explanation: ''We are first and foremost movie critics. That's all we do. We don't do talk shows. We write about and think about and see movies all the time. Seeing professional people do anything is always entertaining.''

Roger, his feet up on the table, is having his makeup applied - little pink triangles of blush - which makes it difficult for him to match Gene quote for quote. Gene continues filibustering. ''I think our criticism is understandable. . . . The problem with a lot of other film criticism on television is, you get one voice looking out at you from your screen. And after a while you think, 'What does he know?' Here, you've got the other person, your own voice, sitting right next to him saying, 'Hey, what do you know?' ''

Which is, one gathers, one of their favorite ways of addressing each other.

Still the editing room, a half hour later. Gene is waxing eloquent about his background.

Gene: ''At any rate, then I got in the Army and they asked me if I wanted to be a truck driver or a cook or a journalist. I didn't take too long to pick journalist.''

Roger: ''You made the wrong choice.''

Gene: ''I could have been threatening Julia Child if I'd gone the other way. Or I could have had a show called 'This Old Truck.' ''

Roger: ''We could have 'Sneak Recipes.' ''

Gene: '' 'Sneak Souffles.' ''

Roger: ''You always read in Gene's biography that he was a philosophy major at Yale. It never mentions that he also learned journalism in the US Army while working in the typing pool.''

Gene: ''But I had a 10-week course.''

Roger: ''He spent 10 weeks in the Army and four years in Yale. He learned so much more in the Army than he did at Yale that he went into newspaper work. He turned down six jobs as philosopher. They wanted him to go places and be a philosopher. You were offered the position as the top of three different mountains, weren't you?''

Gene: ''Rog, how would you like to go get a sandwich?''

Roger would not. Besides, it is fast approaching the time when the two actually get down to work, or rather move down to the basement, better known as ''the set.''

Here, under the blaze of studio lights, the two stars sit on the burgundy velveteen seats and practice running through their scripts on the video prompters. ''Our first movie tonight . . . ,'' Roger obediently reads. Not surprisingly, Gene decides to harass him. ''Keep going, big guy. Just keep talking as if I'm not talking.'' Roger obliges him: ''This film takes place . . . .'' ''Oh, it doesn't bother you, does it?'' crows Gene.

Their producer has no time for this kind of exchange. ''Did Roger straighten his collar? I should have pinned it. More makeup for Gene. Smile, Gene, you're so handsome. Does Roger have the right glasses on? OK, open the dog's mike. Quiet the boys.''

Just try to.