A weary Tom Selleck stands gun in hand in a riverboat as it rounds a bend in a mosquito-ridden river and slides onto a muddy beach.

Glancing to his left and right as though looking for a hidden enemy, Selleck leaps ashore in pouring rain, races up the beach and comes to an abrupt halt -- before 100 waiting, soaked fans shouting "Tom, Tom, we love you, Tom."

Birds take to the air in panic and a family of ducks waddles back into the river. Selleck puts aside his river "war," laughs and politely waits while the crowd, held back by a security guard, takes its photographs.

Selleck, who stands 6 feet 4 inches tall and moves with the smoothness of an athlete, has become for millions of television and film enthusiasts a sex symbol of the 1980s, a star who cannot stop working.

In an age where stars such as Dustin Hoffman and Dudley Moore sometimes have trouble looking over the shoulders of their leading ladies, film experts are hailing Selleck as a throwback to the days of John Wayne and Gary Cooper.

Selleck, filming another episode of his hit television series "Magnum, P.I." on the Hawaiian island of Oahu, was supposed to be searching for an old Vietnam comrade in the jungle swamp when he was stopped by his fans.

But that was nothing new. It is commonplace for women to throw messages over the wall of the mansion in which part of the series is filmed.

Selleck can no longer film in the Waikiki area of Honolulu because of the crowds of fans, mostly from the United States and Australia, who want to touch him.

And he had to stop driving a red Ferrari, similar to the one seen in the series, because crowds trailed his car. A woman who won a state lottery in Michigan said one thing she would like to buy with her millions was Tom Seleck.

But in the peace of his mobile trailer home on the set, Selleck talks of his fear of becoming burned out by work and his efforts to remain a normal human being under the pressure.

"My eyes become bloodshot a lot these days," he said. "If you are working six days a week, 12 hours a day under the kind of arc lights we have to use, they are going to get that way.

"I have been working four years straight now. I'm getting to the point where I worry that I will become so burned out that it will start affecting my work."

Selleck's third starring film, "Runaway," in which he plays a poker- faced police sergeant fighting a computer genius and death-dealing mechanical spiders, is currently in theaters in the United States. His previous starring films were "High Road to China" and "Lassiter." His television series, in its fifth year, is being shown in 73 countries.

"I have always been able to push myself because I play a lot of sports, mainly volleyball now, and from that you know there is something deep inside you on which you can draw," he said. "I know there are traps, such as booze and drugs, but these things don't interest me.

"And I am not complaining. Nobody offered me these films before I got 'Magnum' and I would be stupid not to accept them."

"By the time I'm going into a picture I'm a bit worried because I don't feel particularly rested," he said as he gnawed at pieces of roasted chicken. "The adrenalin has to start pumping and that is what keeps me going."

Interviewing Selleck is at times more like interviewing Tom Sawyer than Thomas Magnum. "I don't think I should talk about personal relationships. It's like kissing and telling," said Selleck, who is 39 and divorced from his first wife, Jacquelyn.

"My mum always said, 'Don't do it -- it's not nice, Tom," he added with a grin. "I will tell you this -- I am involved with someone right now. I have been seeing somebody for sometime.

"But the private part of me is where I work from. I expose some of that part in my work every day."

Selleck continued: "I would like to think I would have the courage to say I have paid my dues and maybe I can take a little time off at the end of this television season. If you get burned out you don't have anything to give.

"I have a deal to do 'Magnum' for seven years. Maybe after that nobody will want me to do a picture. Maybe 'Magnum' will be the best thing I ever did."

Many stars at Selleck's level of fame would have found ways to end their television contract to concentrate on films. "I stick to my word," Selleck said simply.

He agreed the pressure of fame had changed the way he lives. "I like the fan attention sometimes . . . But I now choose a restaurant by how much I will be left alone rather than by the food.

Selleck said he was influenced by actors he grew up seeing, such as James Stewart, Henry Fonda, Cooper and Wayne. "Of all those people, I would probably go to a John Wayne picture first," he added.

"I'm dying to do a Western. I was asked to do one but I couldn't because I was doing 'Magnum.' It just killed me.

"This sort of thing happens a lot and it is frustrating," he said. "But 'Magnum' is hardly a cross to bear. It may be the most wonderful thing in my life . . .