WHEN Carol Channing is mapping out a theatrical tour, she has a simple formula for deciding which cities and which theaters to play. Wherever Yul Brynner has been, she follows -- because, to quote Brynner proudly quoting Channing, "I know that the leading dressing room will always be in perfect condition."

The latest dressing room to get a Yul-a-haul is at the Warner Theater, where "The King and I" starts previews Wednesday night, 30 years after Brynner and the King of Siam become associated. The Warner management has added a new paint job and carpeting and curtains, while dispensing with a wall or two in order to create a bona fide "star suite."

This is a small-scale renovation compared to what London's Palladium Theater untertook two years ago. The Palladium spent $70,000 installing, among other items, a Jacuzzi and an electrically-operated massage chair -- or so Variety reported in a story described by Brynner as "very misleading."

"This is one of those funny things," says Brynner, his impeccably enunciated words still coated in the ambiguously Eastern accent that has survived the four decades since he first reached Western shores. "I simply laugh at it, you see, instead of being offended. There are very simple reasons for these things. Nothing is done out of star vanity or luxury. It's a three-hour show, you see. Very few people are aware of the fact that when you play a part such as the king, 85 percent of your waking hours are spent somehow on that play. To be able to go on playing without being embittered or over-tired, you can't live in shabby, rundown conditions. The money that was spent on doing that dressing room was part of a whole program. The Palladium Theater backstage was terribly rundown. They decided to make a star dressing room for the Palladium Theater, not for Yul Brynner."

And besides, it wasn't a "Jacuzzi," says Brynner. It was a "whirlpool."

Fit and trim at 64, Brynner talked about his career last month in a generous suite provided (for the interview) by the Westbury Hotel, where he periodically engages work space away from the commotion of his family's New York apartment, two blocks distant. He was about to plunge into rehearsal with his seventh major Anna, Patricia Marchand, and his sixth district supporting company (although cast members have been retained from the 25th-anniversary revival launched in 1977).

In person, he is smaller than you would expect of such a commanding presence. But as his voice booms imperially forth, it is easy to picture an obedient throng at Brynner's feet, "bowing like lowly toads," and not so hard to believe this is a man who routinely plays 4,000- and 5,000-seat arenas without a body microphone. (The 2,000-seat Warner is a cubbyhole by Brynner's standards.)

He wears black. He always wears black. "That way, there is no possibility for vanity," Brynner explains, taking a sip of the sparkling water he has ordered in keeping with the Spartan, "almost monastic" life style he views as essential to his craft. But like the original Spartans, Brynner has shown a consistent ability to look out for his interests. In April 1975, for example, he contacted a White House acquaintance to urge a military aircraft of Vietnamese orphans out of Saigon, because the future Melody Brynner, then 3 years old, was among a group of children slated for adoption in the United States.

When her Air Force plane crashed, Brynner and his wife, Jacqueline, had an anxious few days before Melody turned up safely in Honolulu. And when her journey became stalled at a refugee camp in San Francisco, Brynner, in Boston Rehearsing the Erich Segal-Mitch Leigh musical of "The Odyssey" (to bear the unforgettable title "Home Sweet Homer"), sought help from Hugh Hefner.

"I suggested that he use his black airplane for something good for a change," Brynner recalls. Hefner obliged by supplying not only the plane but 30 Playboy bunnies to act as nurses, escorting a cargo of orphans to their adoptive homes across the land.

Then came the time Brynner and two friends contracted an ailment diagnosed as trichinosis, after a meal of spare ribs at Trader Vic's in New York. They promptly sued for $3.5 million "because I think trichinosis is a very dangerous thing," he explains, "and because restaurants in general should take an example from kosher food." Although Mrs. Brynner had not been present at the suspect dinner, she joined the suit, asking $500,000 for the loss of her husband's companionship. The illness had "damaged and altered" their marriage, Brynner explained. Eventually, the suit was resolved by what he calls a "very satisfactory" settlement.

People are under the erroneous impression that Brynner has been appearing in "The King and I" continuously for the last 30 years. Actually, he has given a mere 3,046 performances, scarcely equivalent to 7 1/2 uninterrupted years, a figure that will climb to only 10 or 11 years when the current "King and I" tour comes to an end in 1984 or so. Brynner is quick to list the other satisfying roles he has played -- among them, Dmitri in the movie of "The Brothers Karamazov" and the gunslinging robot in "Westworld." But "I know people think of me as just the King," he says.

"How do you play eight performances a week for so many years?" he asks.

And he answers: "I don't believe anything is ever the same. The only way it can be done is to start everything anew. I believe our lives are like that. It applies to us as civilians as well as artists. No two days are ever really alike, if we're intensely aware and searching as I think we ought to be."

There is also the matter of financial remuneration. "Tourins is a very rewarding business in America," says Brynner. He does not say just how rewarding, but he is said to have earned as much as $50-60,000 a week during his late Broadway stint, and Rex Harrison and Richard Burton are said to be generating income in a comparable range as they tour with "My Fair Lady" and "Camelot" respectively. Not by coincidence, both give Brynner credit for, in his words, "the idea of going back and doing what were landmark performances in the history of Broadway."

Incredibly, Brynner has never missed a performance, although an understudy had to finish for him one night in Los Angeles 25 years ago after he fell and injured his nose. Fortunately, Cecil B. DeMille was able to recommend a plastic surgeon who put the nose back together in time for the next show.

If Brynner's accent seems hard to place, it is small wonder. He has spoken 11 languages at one time or another. He was born on Sakhalin Island, between Japan and Siberia. His father was half Swiss and half Mongolian. His mother, who died as he was born, was "pure gypsy from Bessarabia." Brynner grew up in the Far East, later went to live with his mother's family in France and joined the circus as an acrobat, until a bad fall that left him, at 17, with a chronically troubled back and a career in limbo.

The next steps were London, the theater, and New York. He became a director with CBS' "Omnibus" in the primeval days of television, and co-starred with Mary Martin in "Lute Song," an esoteric musical based on a 14th-century Chinese play. The show ran only a few months, but Oscar Hammerstein saw it and thought Brynner was impressive.

"How he thought that, I'll never know," says Brynner. "I thought I was terrible."

Right or wrong, Hammerstein remembered Brynner, which led to his being cast in "The King and I," which led to one of the strongest associations of one actor and one role in theatrical history.

In February 1951, when "The King and I" opened in New Haven, "It was a disaster," Brynner recalls. "It was almost five hours long. There was nothing but conflict between Anna [Gertrude Lawrence] and the King. There was no such thing as 'Shall We Dance'. . . Rodgers and Hammerstein understood immediately that unless there was an underlying fascination with each other, then there really couldn't be a fascinating show."

By the middle of the Boston run, the authors had made drastic cuts, while inserting "Shall We Dance" and "Getting to Know You" (a tune discarded from "South Pacific"). And when "The King and "I opened at the St. James Theater on March 29, Variety reported that the show "held the first-nighters enthralled, even minus the almost inevitable spring coughing."

It stayed put on Broadway for 1,246 performances. It chugged merrilly on to Chicago. It devoured Los Angeles. It conquired London. The movie won Oscars for itself and its star, even though Brynner had to compete with Brynner in "Anastasia," another Twentieth Century-Fox release of the same year. ("I almost lost my Oscar through the stupidity of those people," he recalls. "That's why they're called Sixteenth Century-Fox.")

And ever since, as the King would say, it has been one long case of "Et cetera, et cetera, et cetera."