Sneakiest thing you ever saw.

All over America, for the past few weeks, unsuspecting moviegoers have been, as usual, unsuspectingly movie going. Settling back in the pre-feature dusk amid the reassuring rattle of mint and Milk Dud wrappers, they wait in hopeful expectation for a well-produced fire-code slide (Smokers Will Be Subpoenaed By Congressional Subcommittees), a sexy coming attractions trailer, a heartwarming list of credits and titles, and who knows, maybe even a half decent movie.

And, mid-clutter, they see this: some cutesy pie animation, followed by a shot of wristwatches on parade with voice over babbling about. "The gift you'll be proud to give or receive."

Huh? What was that again? Could it have been . . .

Merely remembering the scene, a shudder passes through me, the shrieking theme music from "Psycho" springs unbidden to the mind and a hideous word forms on my lips as the subtle horror of the moment is reborn:

Commercial.

Commercial? There in the pristine temple of Bergman.Antonioni, Bertolucci, Fellini and Clint Eastwood?

As Gary Cooper used to say, implying in one compact eructation a fatalistic acceptance of all the suffering the universe is capable of dropping on human shoulders. "Yup."

The movie commercial is upon us. Even now, the Lindbergh of film advertising, an innocuous 30-second spot for Seiko quartz watches, whatever they are, is landing on retinas in 1,800 movie screens around the U.S. Has been since Oct. 26. The perpetrators, a Paris-based outfit named Screenvision, say there shortly will be a sister ad (some perfume) making the rounds. Then, after a discreet interval, two more spots for a total of four: That is two minutes worth of sell.

Meanwhile, a second company based in Nashville - this one is called Cinemavision - will begin slinging three-minute ad blocks to 4,000 theaters by the first of the year.

There are moments that slip by almost unnoticed which, viewed in retrospect, prove to be great watersheds of history. This, I fear, may be one of those moments. An ear has ended, one we may look back on as being as prue and innocent as early Mickey Rooney.

It's true that there have been commercials on the movie screen before. Charity pitches for the old actors home - annoying but forgivable. And theaters here and there have accepted ads from neighborhood merchants, usually in the form of still slides. But these were exceptions, local and not pervasive.

And it's true that in the cinemas of Europe, commercials are old hat. Screenvision's been at it there for 40 years, the ad blocks sometimes run up to eight minutes and even Jean-Luc Godard's Maoist audiences presumably take it sitting down.

But this ain't Europe. No. This is the land of freedom and democracy and hope for a golden tomorrow. This is the land of Lincoln and Lovelace. Here there's been a kind of unwritten law: Tv commercials we grumble over but tolerate. Because TV is supposedly free and the sponsors foot the bill.But movies we pay for directly. So we have the right to expect better quality. And to have nothing heavier than popcorn or Milk Duds pushed on us.

I know all that is true because I distinctly remember learning it in a film strip in junior high social studies. I think it's in the Constitution, or possibly the HEW guidelines.

And yet now we find another commercial intrusion skulking into our lives. Another small but significant shift in the balance between business on one side and art-entertainment on the other. Another three minutes of blather poured down our poor irises. Another horror show.

And here, fellow film freaks, is what we're going to do about it:

Nothing.

The truth is that movie audiences will submit in silence to almost any outrage. Why this is no one knows. If you've ever seen the Cinemasochists of New York for instance, queue up outside the East Side mustsee joints for 45 minutes in a blizzard, you know the meaning of the word patsy. What's a commercial to such buffs.

So I knew what to expect when I slipped into a Times Square movie house last week to witness the atrocity firsthand. Laid down four and braced for the Henry Winkler epic. After a Luis Bunuel trailer that treated the PG-crowd to some R, the Seiko came on.

It's a typical commercial: the usual blah-blah, which years of TV survival have conditioned us to half-ignore. I looked around at the crowd. No cries of outrage. No attempts to organize a rush of the projection booth. Nothing. Possibly a raised eyebrow over in the seventh row. Hard to tell.

The fools, the mad fools, as one character in a favorite old science-fiction movie of mine used to say of the other characters at moments of unperceived menace.

Can they not see what lies ahead?

Karen Black: "You mean to say your instruments show a flock of those giant mutant vampire clams heading directly for downtown Wilmington?"

"Charlton Heston: "I'm afraid so."

Helen Hayes: "Is there time to evacuate?"

Charlton: "No. Only one chance. Must persuade the President to order a Cruise missile launching to intercept. That is, right after this important message."

"Ed McMahon: "Right you are, Charlton. You know, if you want to be sure your dog is getting enough nutrition . . ."

I'll tell you what else is coming: When the import of this thing finally dawns, people will start coming in late to miss the ads. Of course many of them will also miss the start of the main feature. They'll be climbing over knees for the first half hour, being shushed and prodded and first thing you know you'll have mayhem breaking out all over the house with battalions of ushers racing waving their flashlights like Obi Wan Kenobi.

(Which brings to mind an even more terrifying specter: Imagine what we'll have to put up with when the Alpo people decide to hire the "Star Wars" special effects crew for their commercials.)

Now in the interest of fairness (Roy Rogers and Ronald Reagan early imbued in me the spirit of fair play), one should note the promises being made. Screenvision vows that bad will not lead to worse. They say their ad skeins will never go over three minutes, despite the European precedent. Nor will they offend, they pledge. None of the "pound, pound, pound," of TV detergent and depilatory ads, one Screenvision exec insisted to me. Movie ads will be different; a different kind of audience, you see. They speak of, elegant images: a skydiver free-falling through space in rhapsodic parabola to land in a cloud of soft drink. The old soft-sell, they whisper. So painless that, well, "We don't call them commercials," a movie chain official corrected my terminology. "We call them short subjects."

Listen: Carmen Miranda said it best in "The Gertrude Stein Story:" "An ad is an ad is an ad."

We're also hearing this: These are rough times for movie house operators. They need the extra buck they'll get from commercials. Studios are demanding high rentals for films. And there's a "product shortage," it seems, for reasons Gulf Western's computer could easily explain to Milton Friedman, but which elude me.

Certainly one can feel sympathy for squeezed small theater owners. Certainly one can feel even more sympathy for squeezed small theater patrons. That is, us. We're already paying up to $2.50 per eyeball just to get in and a smattering of Milk Duds will run you another 70 cents. And now this.

Golden goose-egg eaters might well keep in mind the old maxim: Movie freaks may not be overly demonstrative, but the ultimate rebeillion is staying home.