Some decades ago before John Hillerman became Jonathan Higgins -- English bulldog to Tom Selleck's springer spaniel Magnum -- he spent most of his days listening to a recorded Lawrence Olivier recite "Hamlet."

One night young Hillerman left his native Texas drawl at home and took his newly acquired English accent to a party. "Hell, John, you sure sound phony," said a former friend. "Phony" is a fighting word to an actor, especially one whose year's voyage from Texas vowels to the actor's coveted mid-Atlantic speech has just been torpedoed.

But that may have been the last time anyone sneered at John Hillerman's Empire accent. "Even the English think I'm English," said Hillerman. They write to Hilerman and say he's a credit to the Empire on Which the Sun Never Sets. They throw presents for him over the wall of a Hawaiian estate.

"Higgins wasn't difficult for me. After all, I'd played a great deal of Noel Coward," he said. He just dried off his mid- Atlantic accent, and became that most English of Englishman, the expatriate who lives away from the idyllic isles. Hillerman has "bean" to England only twice, most recently when a "Magnum P.I." episode was filmed at Leeds Castle. "I prefer to travel at others' expense," he said.

He was relaxing in California, just back from a prodigal-son television special in Texas to celebrate the state's 150th anniversary. Perhaps because of his Texas visit, Hillerman's speech sounded softer than the rapier cut he uses when he plays the retired British military martinet.

About now, Hillerman is on his way back to Hawaii once again to alter his ego to become Higgins of the Sandhurst speech, the autobiogaphical anecdote, the dogged derring-do and the social charisma. He also plays nearly a score of Higgins look-alikes who show up as the Englishman's kin -- the Irish monk, the South American political leader, the Texan and others -- all allegedly the offspring of a peripatetic father. He admits that, as an actor, he enjoys slicing himself up to play more than one Higgins, and gives full credit to the various transformations in his looks to Albert Jeyte, "a superb makeup man, European trained." But he sounds just a bit wistful when he says, "all that hair for the Higgins relatives, that's Jeyte's."

His regard for Higgins might even equal the egocentric's own opinion: "I love doing the character." If Higgins and Hillerman don't have the same nationality, "we do share some characteristics." Actually, Hillerman shares more than initials with Higgins: They're both 50ish bachelors ("I'm not married. Never have been.") with a taste for learning and luxury. Hillerman lives alone in "the second largest penthouse apartment on Waikiki," he said, "4,000 square feet, 10 rooms, tall ceilings, 260-degree view. I looked at 250 before I bought this one. I hope to live in it all my life."

Even with all this space, he doesn't share Higgins' taste for company and expansive parties. "My idea of the perfect day is one spent in bed, reading. I do it whenever I can." The apartment is filled with hundreds of books -- he reads at least two a week -- but no rare collections such as Higgins keeps. They are, of course, hardcover. "I really only like to read and act," he said. Hillerman enjoys the sun and the surf -- from 39 floors above in his penthouse. The weather in Honolulu is "far superior to Washington's," he said. "Only one hurricane in the six years I've lived here."

He leaves more active enjoyment of the Hawaiian paradise to volleyball player Selleck. "He's very athletic. I have never been into that sort of stuff. And at my age, I also like to stay out of the sun.' He enjoys kidding Selleck about the time the lead player and his guest star were dressed to the teeth for a love scene on the beach, when a big wave came along and drenched them.

But Hillerman was on the other end of the laugh during shooting of one episode in which Higgins is conked on the head and wakes up to imagine himself a Shakespearean actor. A dagger, thrown at him by the villain, was supposed to lodge neatly in the tree beside him -- guided by a wire, so no one would get hurt. But this time the dagger stopped during its flight along the wire, right by Hillerman's neck.

Laughs on the set are not the only reason Higgins likes to act in "Magnum." "At its best, a television series is like a repertory company," he said. "And in 15 years in the theater (including from 1964 to 1969 in the Washington Theater Club), I learned to like ensemble acting best. Tom Selleck and I know each other's rhythm so well it all comes easily. Tom is such a charming, unassuming man. He handled instant stardom better than anyone before. I've never worked with a more generous star."

Hillerman speaks highly of the whole cast, including regular sidekicks Roger E. Moseley (T.C., the helicopter pilot) and Larry Manetti (Rick, the club manager). He shares Higgins' admiration for "the lads," the great black hounds that in one scene untied Higgins and handed him -- er, mouthed him -- the telephone. "Though we aren't allowed to fraternize with the dogs," he added. "They're very carefully trained by their owner, Scott Hart. He's very well known in Hollywood. He gets them to do incredible things -- all by hand signals. They are wonderful dogs, friendly and nice."

The cast often works six days a week, though Hillerman is on camera only for three or four. He said in the beginning Selleck sometimes worked 80 hours, "but now they limit him. That was just too hard."

Hillerman agrees with those who think the show is one of the best written on television. "We usually use the sae staff writers. They are tuned in to the characters. But we all have the freedom to say we won't do something if it doesn't seem in character. Sometimes Tom and I, working together, make changes."

Hillerman sees a trend away from one- hour action shows, especially in view of Bill Cosby's "enormous ratings." But he thinks that CBS's shift of "Magnum, P.I." from its slot opposite "The Cosby Show" -- to Saturday this season and to Wednesday in the fall -- will help the show's ratings. "We're not a standard action show, but much more complicated. We try not to have as much gore or car chases. We haven't lost our Ferrari yet. And some of our comedy is bright and clever, damn near Noel Coward."

"Magnum, P.I." is filmed in Hawaii, and Hillerman says the Robin's Nest is actually a fine 1920s estate on 31/2 acres. "A very pleasant woman lives there. We only film exteriors of the house, once a week perhaps. The interior sets, Tom's guest house and my study, are all shot in a studio. Still the owner of the esate earns her rent money: She has to put up with all those fans who gather around the gate day and night because they think Tom and I live there."

Getting from Denison, Tex., to Hawaii was not easy for Hillerman. He went to the University of Texas, majoring in journalism because he had won essay contests, and then joining the Air Force -- only to be sent back to Fort Worth. He became part of a theater group there "because I was tired of the barracks. Sounds corny to say it, but when I first walked out on the stage, I thought, 'I've been bored all my life, right to this moment.' "

In New York, after the Air Force, he soon knew he had to lose his Texas accent. He worked a year with Fanny Bradshaw, a voice coach. "She made you listen to yourself, until you could hear what you were doing." Listening to the Olivier tape was part of the treatment.

During what he calls "a long and difficult struggle as an actor," he played more than 100 leading roles on and off Broadway. "But only in the last 10 years have I made a decent salary. You know, there are 60,000 Screen Guild actors in California, and only 400 earn over $50,000 a year."

Hillerman had $700 in the bank when he left Washington for Hollywood and roles in movies produced and directed by Peter Bogdanovich, who'd been a spear carrier with him in Shakespeare in the Park's production of "Othello." In Bogdanovich's "Paper Moon," Hillerman began his split personalities, playing a sheriff and his brother -- with a Texas accent.

Two television series, "Ellery Queen" and "The Betty White Show," didn't last long. "But soon as I saw Tom in the 'Magnum' pilot, I knew we would make it." Hillerman said he hopes "Magnum" will go on another 10 years. But if it doesn't, he's not worried about finding another series. "Obviously, I'm glad to see the new trend of hiring actors in their 50s and 60s and the success of Angela Lansbury's show ("Murder, She Wrote") and 'Golden Girls.'"

And what does Hillerman watch on television? "Why, 'Magnum P.I.' One has to constantly analyze one's own work."