WHEN MICHAEL CIMINO sneaks a movie, he goes all the way.

A few days ago, the director previewed his controversial $36-million Western epic "Heaven's Gate" in a cloak-and-dagger operation so bizarre that even the film cans were disguised.

It all began on Friday afternoon, Feb. 6, when Cimino, with a hat pulled down to obscure his face, and using an alias, was whisked up to the back door of a Seattle, Wash., hotel and sequestered in a room registered to Jackson Smith.

Behind him scurried a gaggle of United Artists executives who were also using aliases and wearing what they regarded as disguises: brand-new faded Levis and windbreaker jackets.

In the trunk of their rented economy car was the new edited "Heaven's Gate," which Cimino had trimmed to two hours and 15 minutes and which contained some scenes which had been dredged up from footage Cimino had shot and discarded more than a year ago.

Fearing that a bellhop or a chambermaid might betray the movie's title, the reels were carried in well-worn cannisters for the film "The Dogs of War," another U.A. already in release.

"The object was to get the film into full theaters in Seattle and Portland, playing it to audiences who had no idea what they were going to see," said a spokesman for United Artists. "We wanted to show it to people who weren't prejudiced by all the bad publicity surrounding the film."

The publicity could hardly have been worse.Early warnings began to appear in the summer of 1979, while the 38-year-old director was still shooting on location in Montana. There were reports of huge cost overruns, scenes shot 20 or more times, and outrageous expenditures for period props. The film's original budget of $12.8 million swelled to $36 million amid growing studio anxiety.

Finally, after a year of post-production, the 3 1/2 hour verson opened in New York in November of last year. The critics panned it, and United Artists instantly yanked the film out of circulation, pulling prints out of theaters which had paid millions in advance for the rights to show it at Christmas. Speculation began immediately about who would re-cut the film -- and whether the final result would ever be salvagable

All of which explains why Cimino and the studio executives descended on Seattle Feb. 6 to engineer perhaps the most lavishly contrived "sneak" preview in the history of modern cinema.

But the results were disappointing: That Friday evening, the movie played to what U.A. called "a so-so reaction" in a still-undisclosed theater in Seattle's university district.

Far from pleased, Cimino and gang headed on to Portland, Ore., the next day, creating an even more complex scenario that could have been lifted from a Peter Bogdanovich movie.

"Actually it started a couple of days earlier," said Marilyn Jones, promotional dirctor for Portland's KGON radio station. "Some guy using the name of what turned out to be a fictitious research group called me and said he would like the station to give out tickets for a sneak preview." But the caller refused to give Jones the name of the picture, and she turned him down. "This was the first time we'd been asked to promote an unknown film, and we didn't want to get into it."

Unknown to Jones and KGON, U.A. had already rented the Rose Moyer Cinema far out in Portland suburbs, telling the owners that KGON was distributing the tickets. And somehow the tickets did get out, leaving Jones with the lingering feeling that "those guys passed them out at our concert on Friday night anyway, even though we turned them down."

The ticket-holders streaming into the theater that Saturday were greeted with strange faces. The ushers, and even the popcorn girls, had been replace by U.A. officers in mufti. Only the projectionist, up in his sealed booth, was allowed to remain, and even he, until the last fatal seconds, believed he was showing "Dogs of War."

"It's hard for me to explain the fear under which we operated," said a U.A. spokesman. "There were only a couple of people in the whole studio who knew what was happening. And even then, nothing was written down. The guys who went along were given airplane tickets, and told only that they were going on a U.A. mission. When you have a $40-million movie that was derided the first time out, you want people to see the new version without the whole world looking in."

There was hardly any danger of that. Even men conected with the Moyer theater were refused entrance. "I thought they were showing 'Dogs of War,' and I wanted to see it for free," said Bill Christiansen, the buyer for the Moyer chain. "There was an uncomfortable-looking guy at the door dressed in what I would call late Venice, California. And he said to me, 'No ticket, no show.' So I told him I was the buyer for the theater chain, and he answered, 'Especially if you're the buyer. You might not like this picture and then spread it around to all the other buyers.'"

So Christiansen shoved off. But he kept wondering what kind of movie it was to make them so uptight. Later, when he found out what it was, he said to himself, "Oh, sure."

In the days that followed, the same sneak scenario, varying slightly each time, was played out in Denver, Kansas City, Pittsburgh, and Chicago. "'Heaven's Gate' still has to be polished a bit with some dubbing, but I think it is really a great picture now," said Tom Gray, the major U.A. publicist on the West Coast who has followed the film through its bumpy course.

As Gray was speaking last week in his Hollywood office, the Cimino debacle and other problems were creating corporate earthquakes through the U.A. system.

Last Tuesday, the new U.A. president Norbet Auerbach, announced to exhibitors attending a convention in Reno that the studio is "facing a crisis in control, with plenty of works for us to do." Two days later in Hollywood, Auerbach succeeded U.A. Board Chairman Andy Albeck, who said, through spokesmen, that he was "retiring early." The same day U.A. announced that American rentals on its pictures had nosedived from $183 million in 1979 to $112 million in 1980. It's interesting to note that U.A. said a year ago it expected "Heaven's Gate" to make $60 million during its first two months of release. This, of course, would have made up the U.A. profit loss.

But that was before the film was pulled -- canceling what would have been a record Christmas booking for U.A., and obliging the studio to refund more than $100,00 in advance sales in New York alone. Cimino, under close scrutiny from U.A. brass, began reediting the film the day after the preview. sTo date, no critic has seen the new version. But Tom Gray said optimistically: "Some audiences, especially in Portland, loved the film. In Portland they stood up and cheered."

"Wel, I don't know about that," said Marilyn Jones, who is still hunting for members of the nonexistent research company. "I haven't been able to find a single person who saw it. And that's kind of wierd because Portland isn't that big a city, and you would think a radio station would have heard something."