Who doesn't dream of living on a beautiful, balmy South Sea island?

Try this one: Norfolk Island. About three miles in one direction and five in the other. Just an old volcano about 1,000 miles off the east coast of Australia. Just an old volcano with a climate like a transplanted Camelot.

Novelist Colleen ("The Thorn Birds") McCullough lives there. Just the place for a best-selling novelist to hide out.

Climate? "Oh," she tosses off, "perfect. Never gets colder than 55 or hotter than 85.

"Believe it or not, it mostly rains at night. It's true, it's true . . . "

Norfolk is green with tall hardwood trees that were mistaken as pines by early sailors. It is, says McCullough, "very beautiful physically. It rises to over 1,000 feet. It is hedged in by these absolutely massive cliffs that the sea just breaks against. It has a small coral reef at one part of the island, and there are four perfect beaches . . . "

Its inhabitants screen new residents carefully, and rejection is not uncommon. McCullough says it took her nine months to persuade them she "wouldn't throw my weight around."

She could have done with less fame and riches, she says in her broad Aussie tones. On the other hand, if "The Thorn Birds" hadn't been such a bottomless well of fame and wealth, she probably wouldn't be spending some $6,000 a year on other people's books, nor would she be reading them on Norfolk, now would she?

Some people might have smiled smugly at that, but Colleen McCullough doesn't just smile. She laughs. She laughs a great deal. It is the kind of laugh that wells up from the bottom of her feet, it seems, and bubbles musically up about six full tones and maybe 50 decibels until it explodes in joyous ostentation. Heads always turn when Colleen McCullough laughs.

She can never hide, she says, because of that laugh.

It would be hard for her to hide, in any case, this neurophysiologist turned novelist. She is tall, about 5 feet 10, and endowed with what current euphemism holds to be a "gifted" figure, some 200-pounds-plus of it.

She wears her long, strawberry-blond hair piled high on her patrician head. It frames delicate features that would as soon fit a Camille. Colleen McCullough, who is 44, is wearing a billowing lime-green silk Shantung shift and her hair is tied with a peach and lime flower-print scarf. She is picking at a tuna fish sandwich and talking about her own decided satisfaction with her life and the "silliness" of most women when it comes to men.

She has just published a new book, "An Indecent Obsession," which has zoomed to the top of best-seller lists. She is taking a quick trip around the world to see it properly launched.

The books and their author might be called "fast reads." The veteran of a string of romances -- she calls it her "chequered" (she pronounces the "q") love life, though it includes no marriages -- McCullough is bemused by the female attitude toward the male. "I mean," she says, "even the most intelligent woman can fall to pieces over some man, and you think, 'Why? He's such a twit.' "

"I was weaned on romances," she confides, which should be no surprise to anyone who has read any of her books. The latest, about a few tense days in a mental ward of a post-World War II Australian army hospital, is something less of a potboiler than "The Thorn Birds," but her heroine, a nurse named Honour Langtry, manages to almost fall to pieces over some "twit," anyway. The newest book is intended to be somewhat deeper, and is quite a bit shorter than its predecessor, but not all critics agree that the former is indeed the case.

What matter. "The Thorn Birds" has sold some 9 million copies, hard and paper, and been translated into 17 languages. It will soon be a TV mini-series starring Richard Chamberlain. "An Indecent Obsession" had four prepublication printings totaling 200,000. And a film version of "Tim," McCullough's first novel, will be released any day now.

McCullough's early school days in Australia were during the war ("We always expected to be invaded. We hated Winston Churchill's guts. Never forgave him for saying, 'Let the Japanese invade Australia; we'll get it back later.' ") Later, her father was a sugar cane cutter, among other things, and she grew up in a family that was thoroughly "outback" and usually more or less miserable because her parents' marriage was more or less miserable. The family ended up in Sydney.

She says that she's the "only intellectual in a family of jocks." Her mother at age 74 is a mountain climber, for example, but Colleen McCullough is perfectly happy to leave physical activity to others. She is "not concerned," she says, "about my body." She proves this, among other things, by smoking one cigarette after another. "I love my cigarettes," she insists, a bit defensively, "and why should I give them up any more than . . . I like acres of white sugar in my coffee. I don't have children or a husband. There's only me. So I figure it's my choice and I just don't like the thought of having to worry about my body. Without cigarettes I'd probably be arrested for sex crimes or something. Pause. That," she pronounces, "is a ma-a-a-rvelous way of shutting people up when they criticize me for smoking. I just say it's an oral fixation."

She was always a literary omnivore, reading in her early adolescence at the rate of about 14 romances a week. "They were so clean, I couldn't be corrupted by romances," she says. "So that's what I was permitted to read."

She graduated to adventure stories and science fiction. Her book habit is still probably her most expensive -- cigarettes are a close second -- but she spurns such best-selling authors as James Clavell and James Michener -- "formula books," she sneers. She does not consider herself a writer of formula books. Toni Morrison is her current favorite.

She trained as a nurse and became interested in neurology. She worked in hospitals in Sydney and later in London, where the head of the Yale Medical School department of neurophysiology persuaded her to move to New Haven.

She decided to move back to Australia because her family -- her mother and her uncles -- was becoming frail and it "isn't easy to get 10,000 miles at the drop of a hat." Also, of course, the success of "The Thorn Birds" made it impossible to continue her scientific work, which, she says, "has to be anonymous."

On Norfolk, she will satisfy her scientific bent with a telescope and "an amateur seismographic station" she is setting up.

She moved to the island "in an act of self-preservation as a writer." It seems, she says, as though it were the most natural thing in the world, that in Australia "I am something of a national heroine, because a lot of people there seem to think I put Australia on the map. When 'The Thorn Birds' came out, things like 'Breaker Morant' or 'A Town Like Alice' or even 'Prisoner in Cell Block H' hadn't happened."

McCullough seems to have it all her own way -- the popularity, yet the solitude of the island. With her on Norfolk, she says, are "two cats, and I have Kevin, who does my g-a-a-arden, and Trudy, who cleans my house -- she's Dutch and looks like a Playboy centerfold -- and Mary, who's my secretary, and so I'm not alone. But my life is my own and I like being in a situation where the people I'm surrounded by don't have emotional holds over me."

Aside from the island, the telescope and the book habit, Colleen McCullough sees her needs as modest. As for her mother in Sydney: "Ah," says her daughter, "she's much more gone on the whole famous-writer business than I am. And she flashes jewels like mad. It's wonderful. She is," the daughter says affectionately, "bush, bush, bush . . . "

And Colleen McCullough laughs and laughs.