An Eye for Detail That Commands a Sea of Respect : Books: Patrick O’Brian sets his tales in the Royal Navy during the Napoleonic Wars--and he stays faithful to the dialogue of the time.

“It has, then, no zygomatic arch?” asks the 81-year-old writer as he contemplates the fossil skeleton of a Smilodon fatalis , the saber-toothed cat, in the George C. Page Museum at the La Brea tar pits.

Is it the lack of the cheekbone arch that permits it partially to unhinge its jaw, the better to use its two terrible ripping fangs?

No, the curator explains that it does have one, indeed, and presently hands him an S . fatalis skull so he can examine its hinge.

Patrick O’Brian, the Irish English author (and amateur naturalist) whose books sell 300,000 to 400,000 a year in this country, flashes a bright smile of delight. He has again learned something new, which just might, someday, find a spot in the continuing series of novels, now numbering 17, he has published since 1970.

The books are set in the Royal Navy during the Napoleonic Wars and written in dialogue, vocabulary and rhythm that are remarkably faithful to the English of that time. Slow to catch on at first, they have become so popular that the publishing world speaks of “the O’Brian phenomenon” when describing the surge of fame and presumably fortune that have lifted this small, frail-looking writer.

There is an O’Brian newsletter. An O’Brian guidebook has been commissioned. There will soon be an O’Brian CD. And the first O’Brian movie is in the works.

And there are increasing numbers of passionate O’Brian fans, whom he encountered on a monthlong tour of the United States on publication of his latest novel, “The Commodore” (W.W. Norton, 1995).

In San Francisco he spoke to a sold-out audience of 900, nearly all of whom appeared to have read each of his novels. At UCLA a standing-room-only audience of 400 listened as Charlton Heston, a fan of years standing, interviewed O’Brian and read a passage from one of his books.

The series has two principal characters. One is Jack Aubrey, a straightforward, skillful, rather bluff but immensely likable English commander. The other is Stephen Maturin (pronounced MAT-uh-rin), an Irish Catalonian who is an enthusiastic naturalist, a physician and a part-time spy for the English against the hated Napoleon.

Maturin becomes the doctor on Aubrey’s ship, the two become fast friends, and so remain through thrilling and suspenseful battles and other dramatic sea adventures, love affairs, marriages, financial reversals and good fortune.

Aubrey is a strong, brave leader at sea, less successful on his land legs. Maturin still, after all these years, has not learned the nautical names for things and falls down and sometimes overboard, but he is the more subtle.

A reader at the San Francisco event, at which O’Brian was skillfully interviewed by poet and UC Berkeley English professor Robert Hass, who has since been named poet laureate of the United States, wondered if Aubrey and Maturin were two aspects of the same person, as has been said of King Lear and the Fool.

“No,” O’Brian replied, “I look upon them rather as positive and negative, the exchange between which expresses what I wish to say.”

The obvious comparison for O’Brian’s books is C.S. Forester’s Horatio Hornblower series about the Royal Navy. “He did brilliant descriptions of action, which I can’t match, but his characters are a little flat,” O’Brian said in San Francisco with an elfin smile of playful disingenuousness.

O’Brian deprecates himself too much. His sea actions, which he plots with rulers to get the sailing just right, are among the finest in all literature. His portrayal of the sea brings it alive.

O’Brian’s study of character, in his two principals and in their wives and others, is both sympathetic and complex. In the San Francisco audience, teacher Rick Risbrough said he finds the understanding Aubrey and Maturin have of each other one of the most attractive aspects of the series.

“Their mutual respect and civility is most impressive,” he said.

Francis Kent, a former Times foreign correspondent and editor who has read the whole series, is more direct: “To me it may be absolutely the best fiction I’ve read. So knowledgeable, so beautifully written, so gentle. None of that trite, vile roughhouse stuff you see everywhere you turn.”

O’Brian’s appearance at UCLA was appropriately sponsored by the Friends of English. He explained there and in San Francisco that in his youth, when he was sickly, he read deeply and widely in English prose of the 18th Century: Smollett, Swift, Richardson, Fielding, Johnson, Gibbon. . . .

“That was the reading of my youth. What you read before you are 20 or 23 you read with an astonishing intensity. . . . Gibbon wrote a most noble English . . . it has a roll and a splendor.”

These writers, with Jane Austen, made the forceful, rolling English that O’Brian has recreated in his novels. These are the first two paragraphs of “The Commodore”:

Thick weather in the chops of the Channel and a dirty night, with the strong north-east wind bringing rain from the low sky and racing cloud: Ushant somewhere away on the starboard bow, the Scillies to larboard, but never a light, never a star to be seen; and no observation for the last four days.

The two homeward-bound ships, Jack Aubrey’s Surprise, an elderly 28-gun frigate sold out of the service some years ago but now, as His Majesty’s hired vessel Surprise, completing a long confidential mission for Government, and HMS Berenice, Captain Heneage Dundas, an even older but somewhat less worn 64-gun two-decker, together with her tender the Ringle, an American schooner of the kind known as a Baltimore clipper, had been sailing in company ever since they met north and east of Cape Horn, about a hundred degrees of latitude or 6,000 sea-miles away in a straight line, if straight lines had any meaning at all in a voyage governed entirely by the wind, the first coming from Peru and the coast of Chile, the second from New South Wales.

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O’Brian is by no means a mere antiquarian, but a writer of strong and rhythmic prose. He has written a well-received biography of Picasso, which the late art historian Kenneth Clark called “the best”; some earlier novels; short stories; translations from French, including Simone de Beauvoir, and a fine biography of the botanist Joseph Banks, who sailed with Capt. James Cook and later was president of the Royal Society.

The Banks biography was a nice fit for O’Brian, combining the time in which his series is set, a famous sea voyage on a Royal Navy ship and the intense explorations of a naturalist.

On his recent visit to Los Angeles, O’Brian was greatly pleased with the tar pits and their museum. He was especially happy to view the skeleton of the extinct Glossotherium harlani, the giant sloth; Maturin, like his creator, is particularly fond of sloths, both two-toed and three-toed, and is always on the lookout for them.

Afterward, the writer and his small, soft-voiced wife of many years, Mary, walked in the park; together they poked sticks in the little tar volcanoes bubbling up in the grass. “It is truly awesome,” he says of his visit. His guide, Cathy McNassor, was deeply impressed by depth of his knowledge of the details of paleontology.

It would not be surprising to find some souvenir of the tar pits appearing in a future book. O’Brian’s work is full of the finest detail about sailing, naval warfare, geography, nature, medicine and whatever his curious mind picks up. He rarely explains the nautical terms he uses, of which orlop of crossword puzzle fame is one of the simplest. Many of his fans keep a dictionary handy.

Some add to that an atlas to follow Aubrey and Maturin back and forth across the waters of the world, although, “If you read the prose carefully,” O’Brian tartly told his UCLA audience, “you don’t need maps.”

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It helps, though, to have a knowledge of music. Aubrey and Maturin meet in the first novel, “Master and Commander,” at a concert in Port Mahon on the island of Minorca in the Balearics. The musicians are just finishing the first movement of Locatelli’s C major quartet. Big, bluff Aubrey is a naval lieutenant in his 20s; Maturin, a civilian of uncertain age with a tongue tending to sharpness:

[Aubrey] leant back in his chair . . . sighed happily and turned towards his neighbor with a smile. The words “Very finely played, sir, I believe” were formed in his gullet if not quite in his mouth when he caught the cold and indeed inimical look and heard the whisper, “If you really must beat the measure, sir, let me entreat you to do so in time, and not half a beat ahead.”

After this unpromising opening the men discover their love of music--Aubrey plays the violin; Maturin, the cello--and so begins a friendship that deepens with the decades, during which they often while away idle hours at sea with the consolation of Boccherini and the like. A CD is being recorded so fans can listen to Aubrey’s and Maturin’s favorites as they read.

Perhaps O’Brian’s publishers should open a travel office. Cynthia Dwork, a mathematician in San Jose, says she has planned some of her travel so that she can visit places where the novels’ heroes have been, like Cadiz, in Spain.

Actually, O’Brian has not traveled nearly as widely as his meticulous descriptions suggest. At UCLA he said, “No, I have not been in the high Andes; I have not even been in the low Andes.” For his Andean portrait, he drew heavily upon Darwin’s “The Voyage of the Beagle,” which he calls “a noble piece of work.”

He is almost always asked how he writes. The O’Brians have lived for many years in a village in southern France in the foothills of the Pyrenees, close to the Mediterranean and Spain. He has a writing room there, and after breakfast writes for several hours, in longhand. A secretary types it for him, and he corrects. After lunch he reads and does correspondence. Sometimes, when he awakens at 3 a.m., he will drive to a high mountain road and walk in the dark, and then the next turn in the narrative becomes clear.

At UCLA a woman complimented him on his women characters and, remarking that he seems to have kept himself “locked up” for many years, asked how he gained such insight.

“But,” O’Brian said with that bright smile that explodes across his face, “I was at one time young!”