GORDON PRANGE, an instructor in history at the University of Maryland, was working in his College Park apartment that brisk Sunday afternoon while his wife went out for a walk. The people who, in their various ways, were to shape much of his life for the next nearly 40 years -- Yamamoto, Fuchida, Genda -- were on the other side of the world at Pearl Harbor that Dec. 7, feeling a euphoria they would never quite feel again.

The mainspring of the attack was the Japanese Navy's air force, and the next day one of the planners wrote in his diary with exultation, "Oh, how powerful is the Imperial Navy!"

It was indeed. Two tidal waves of warplanes from Japanese carriers overwhelmed the U.S. base at Pearl Harbor in that early morning 40 years ago. When the little more than two-hour attack was over, there were 2,300 U.S. fatalities. Only 43 of the 126 planes parked in neat rows at Wheeler Field remained, and only six had struggled into the air to fight. The harbor was littered with the burning hulks of such American ships as the Arizona, the Nevada, the Oklahoma, the Pennsylvania and the Shaw. And the Japanese had lost only 100 men.

Gordon Prange's reaction to the raid contained as much amazement as outrage. "How did they do it?" he wondered. His curiosity began to burn, and that fire never left him. Pearl Harbor became his obsession, both his demon and his angel. Before he died last year, he'd devoted the bulk of his life to researching and writing about it. But he had never been able to finish his life's work, was never able to finally let it go to a publisher. Now a piece of his lifelong study -- 873 pages -- called, "At Dawn We Slept: The Untold Story of Pearl Harbor," has appeared in the bookstores. The research behind it was monumental. Prange investigated the American side with more tenacity, more thoroughness than any historian before him. He mined the materials not only about the attack but also about its aftermath. He had amassed enough material for four lengthy volumes, thousands of pages of paper and hundreds of hours of taped interviews.

The irony is that if Prange were alive today, we wouldn't have the book at all. His obsession with his subject was so consuming that he couldn't let it go. It took death to unclench his hand. Years before his death, his publishers had given up on him; and his wife, Anne, remembers that there were no interruptions for Prange when he was working on his project. "I made a separate life in part for myself," she said, "because of his immersion in his career. I did a good deal of volunteer work in particular."

But even before publication, interest in "At Dawn We Slept" mounted. The History Book Club picked it as its first choice, the Book of the Month Club made it its first alternate and two other book clubs selected it as well. Among the early reviews, Kirkus called it "responsible, intelligent, absorbing." The

In The New York Times, diplomatic historian Gaddis Smith of Yale characterized it as "a brilliant recreation of the thoughts and personalities of the officers on both sides who fought that day."

The constant revisions of his research did not dim his writing. As he progressed, he made his descriptions more vivid and the action more immediate. He planned the book's structure like a film epic with constant intercutting between Americans and Japanese, between Pearl Harbor and Washington, between land and air.

Yet, one of the most notable things about the book is that during Prange's years of work on it he became virtually binational.He pored over everything about Pearl Harbor that he could put his hands on, including a set of 40 volumes of congressional, naval and military reports. Being Gordon Prange, he not only pored over them, he bought a set of them, wore that set out and then bought a second set. Then, he was able to interview a broad spectrum of participants. At the one end was Adm. Hudson Kimmel, the U.S. senior commander at Pearl; at the other, some of the soldiers and sailors who lived through that day.

But his triumph was in his research about the Japanese side. He couldn't interview the architect of the attack, Adm. Isoroku Yamamoto, who'd died when his plane was shot down in 1943. However, he interviewed nearly all the other major actors in the planning and execution of the Pearl Harbor attack. To them he talked repeatedly, scores of times in key cases. He said once that he'd learned about Pearl Harbor at their feet.

Prange grew up in Pomeroy, Iowa (pop. 830), the son of the village blacksmith. He was endowed with a vast reservoir of energy. In high school he was both a sprinter and a shot-putter. The University of Iowa awarded him a track scholarship, but he turned out to be even better in baseball. A stellar third-baseman, just before graduating, he received an offer from the Chicago Cubs. However, he was as dedicated a student as he was an athlete. He'd been known to do his homework in history while sitting on the bench waiting to bat.

"The Cubs would be exciting but risky," he told his friends. He decided he really wanted to be a historian. He saw history as exciting in its own way, and less risky. Then too, he'd fallen in love with the tall, dark-haired daughter of the head of Iowa's history department. He did his doctoral research in Berlin, Munich, and Vienna; his dissertation lay in the field of German-Austrian diplomatic relations. Awarded his degree in June 1937, he proposed to Anne that they get married immediately. Her father approved of the energetic young man but warned her, "He's goal-driven." Anne Prange remembers knowing from the start that she was marrying a man obsessed with his work. "We spent our honeymoon in California because Gordon had a fellowship at Berkeley to study Russian," she said. "But he studied Russian day and night, taking only the weekends off." Three months after the wedding Prange took her east to the University of Maryland, where he stayed throughout his career.

After Pearl Harbor he served out the academic term and, following commencement, entered the Navy as a lieutenant j.g. The Navy trained him in military government, had him lecture at Princeton on it, and then ordered him to Ft. Ord for Japanese language instruction because of his linguistic skills.

He sailed to Japan with the original occupation forces and was soon assigned, as a historian, at MacArthur's headquarters in Tokyo. Mustered out in the summer of 1946, he was invited to rejoin the historical section at headquarters as a civilian. There he rose quickly and soon held a civilian rank equivalent to that of a major general.

The Pranges became known for their hospitality. His historical work on MacArthur's campaigns brought him in touch with a growing number of Japanese officers. At this time most Americans in Japan were either merely businesslike or openly hostile when dealing with the defeated enemy. Not Prange. His interest swelled in Japan's role in World War II and he increasingly invited Japanese guests into his home.

He spoke fluent Japanese. He and Anne fed their guests, paid attention to them, and when they left often gave them presents. Thanks to his and Anne's commissary cards, they could offer their Japanese guests such gifts as bottles of bourbon or boxes of chocolates, sometimes only Hershey bars. This hospitality had a symbolic value and opened doors for him which remained open. Because three-quarters of their guests were Japanese, Anne had some explaining to do to the starchy wives of her American neighbors. But because of their hospitality, Navy Capt. Kameto Kuroshima, Yamamoto's chief staff officer, visited them nine times.

Although he edited MacArthur's reports into four thick volumes, he consistently made time for his own research on Pearl Harbor. What he couldn't do during the day he did late at night. On leaving Tokyo in 1951 to return to Maryland, he took with him a great mound of manuscripts and other materials about the Dec. 7 attack.

The most valuable were the records of his interviews. Because of his position he'd had access to the official Japanese documents about the planning and carrying out of what they termed "Operation Hawaii." However, the documents proved to be a disappointment. They were scant and uninformative. Gradually he learned why. The risk of any raid on Pearl was enormous, and much of its success depended on secrecy. Consequently, the Japanese talked rather than wrote, and when they had to write did so as cryptically as possible. For Prange, interviewing became the answer. Though the bulk of it took place before he left Japan, he continued it for years afterward on a smaller scale. He revisited Japan a number of times and several of his Japanese informants traveled to the United States. The result made "At Dawn We Slept" a model for the use of oral history.

The sources section of the book shows the depth of his interviewing technique. He had 40 sessions, for example, with one of Yamamoto's highly trusted officers, Capt. Yasuji Watanabe, who watched Yamamoto create "Operation Hawaii." He had another 40 with Adm. Sadatosji Tomioka, who knew the naval side of the operation better than anyone else. He had 72 sessions with Cmdr. Monoru Genda, of the First Air Fleet, who stood second to none in the scope of his information. With the leader of the air attack itself, Capt. Mitsuo Fuchida, he had 50 discussions; in addition, Fuchida stayed with the Pranges in Maryland for four months in 1964.

Given the extensive data, Prange labored to create the impossibly perfect book. Though he naturally denied it, the evidence mounted as he grew older. He never could stop revising and amplifying his multitude of manuscript pages.

After he'd been working at it for 30 years, long past the time when the average historian would have mailed his final page to his publisher, Prange was still developing his story. There's a telling bit of testimony in his faculty-review report for the academic year 1977-1978. Annually each member of the University of Maryland's faculty is asked to outline what he's been doing throughout the year. Prange's report reveals no committee memberships, no community service, no professional papers, no awards. Instead it shows his dedication to his research -- and why the manuscript kept growing.

"When I made my Faculty Review last year," he wrote, "I had anticipated finishing both Volumes III and IV of my massive Pearl Harbor study by the end of summer 1977. However, as I studied my manuscript I realized that several important gaps remained."

His wife said that "sometimes over the years past I'd say 'Gordon why don't you finish?' and his answer was invariably, 'There's so much to do and there's so little time.' When after an initial period of optimism he realized that he was going to die, he didn't say anything about its affect on his work. He simply stopped working."

From time to time he turned from writing about Pearl Harbor to writing spinoffs from it. He found enough time to draft three shorter books: an account of the battle of Midway; a biography of Richard Sorge, the Nazis' master spy in Japan, and a biography of Fuchida, the fighter pilot who after the war turned Christian evangelist.

Somehow he found time for his family too. "There was never a day when the children didn't realize that Gordon was working on Pearl Harbor," Anne remarked recently. Notwithstanding, he could be lured outside to play baseball with his children. Baseball always kept its hold on him. On a warm Sunday he sometimes took the family to Griffith Stadium to watch the Washington Senators, while he pointed out how this pitcher could have been knocked out of the box or that batter told to bunt. Athletics in general always seemed to interest him. Especially Iowa athletics. A loyal alumnus, he tried not to miss any of the Iowa football games on television. His son now recalls the vivid afternoon when Iowa's Hawkeyes were beating Michigan's Wolverines till the final minutes. Then Iowa fumbled, letting Michigan tie the game. Prange stood up, strode to the television set, kicked it, and announced bitterly, "I'm going out for a walk."

After his children grew up, he turned to raising roses. He raised them with vigor. He knew little about them at the outset except that they were pretty. But as his part-time gardener Ben Wilson said, "Dr. Prange, he learned fast." Once the back yard had its complement of roses, he turned to the front yard. Soon roses were thriving there likewise. He pruned them, sprayed them, fed them and mulched them. In return he expected results. If one bush failed to flourish, he dug it up and replaced it with a more co-operative bush. By the mid-1970s Behnke's, the biggest nursery in the area, was sending its experts to take a careful look at Dr. Prange's roses.

He taught school with the same zest that he played baseball or raised roses. He made an imposing sight as he marched through the corridors to class. He was apt to have an inquiring student on either side of him, while behind him hurried a couple of teaching assistants with his maps, books and other materials in their arms. In the early 1950s he could keep a class fascinated even on a Friday night. He had one such class, from 6 to 9, in Modern European History. The fraternity men might be in their tuxes and the sorority women in their long dresses, ready for the parties afterward, but they came nevertheless; he was a compelling teacher.

Yet his preoccupation remained Pearl Harbor. Though he couldn't bring himself to publish his major work, he consented from time to time to release parts of it. In 1961 Readers' Digest published a capsule version of "At Dawn We Slept," following it with a condensation of his manuscript about Richard Sorge. The Digest also arranged for a hardcover translation of "At Dawn We Slept" for the Japanese market. In both places it appeared as "Tora! Tora! Tora!," taking its title from the Japanese word for tiger, the signal in the raid that surprise had been achieved and the Americans were sleeping. 20th Century-Fox optioned "Tora! Tora! Tora!" and made it into a movie.

Prange's relations with the Digest were pleasant and profitable for both parties. Not so for his regular publishers. McGraw-Hill had given him a contract as far back as 1953. Over the years they paid him $20,000 in advances and urged him to finish. They even set the first two of his projected four volumes in page proof. He mailed the proofs back with enough alterations and additions to dismay any publisher. He left hardly a page untouched. By 1976 McGraw-Hill cut off communication with him.

Prange simply went ahead as usual till May 1978, when the doctors discovered he had cancer. He did his best to continue. At the beginning his illness dimmed, but didn't extinguish, his energy. During the Christmas holidays a former student and longtime friend, Donald Goldstein, heard what had happened. He'd been a student in one of the Friday night classes and had become a friend of Prange's. Now a professor at the University of Pittsburgh and an experienced military historian, he wrote his old instructor at once.

"How can I help?" Goldstein asked.

"Get McGraw-Hill going again," Prange answered.

After their experience with Prange, the editors at McGraw-Hill showed little interest in getting going again. However, Goldstein was a shrewd, patient negotiator. He finally arranged for a meeting with them in New York. Directly afterward he phoned Prange, "They're through with you, so we've got to compromise." Goldstein offered to provide McGraw-Hill with a single hefty volume, say of the size of William Shirer's "Rise and Fall of the Third Reich," and to provide it according to any time schedule the publisher wished. They agreed but stipulated that they had to have progress reports each month and that Prange should have no hand in the one-volume version.

"The bastards," Prange said, but he confessed that he'd become too weak to do more work himself.

The task of reducing the 3,500 pages of manuscript that had accumulated to a quarter of that was staggering. However, Goldstein contacted another former student of Prange's who had been working with him for some years. Katherine Dillon had started typing for Prange in 1960 and had developed into a top research assistant. A former chief warrant officer in the Air Force, she was both an impeccable typist and a tireless researcher. Ordinarily Prange composed in longhand on sheets of ruled white paper; she transformed the sheets into typescripts.

It was late in 1979 that he turned over the responsibility for the book to Goldstein and Dillon. One day while he was lying in the University of Maryland hospital, Anne took them to the door of his study. They stared in. It was a spacious room, 21 feet long and 20 feet wide. Bookshelves crammed with books lined the walls; file cabinets filled with fat folders intersected the room, and miscellaneous paper and print were stacked high on every horizonal surface including the floor. There was only a narrow path from the door to Prange's desk. It was as if he'd dug his way through a blizzard of paper. The desk, though, was worth the trip, if solely as a symbol. It had once belonged to the eminent American historian Frederick Jackson Turner. When Turner moved from the University of Wisconsin to Harvard, he gave the desk to his favorite young colleague, Anne's father, and her father passed it on to Gordon. Black and battered, it become his prime work table.

Goldstein and Dillon quickly decided not to try to condense those 3,500 typescript pages, in Reader's Digest fashion, but to perform a thorough abridgement. They'd cut, but they wouldn't condense. Though they did major surgery they left Prange's remaining words largely untouched. They added the necessary connectors and curtailed occasional descriptions. They also footnoted. Prange's reputation as an authority meant that his volumes probably wouldn't have needed exhaustive annotation. However, they felt obliged to annotate every important item. They had one advantage: Dillon knew where most things were.

Prange died in May 1980 at the age of 69. Two days before his final stay in the hospital he said feebly, "Let me see some of what you're doing," but he never did. To the amazement of McGraw-Hill they beat the deadline by a month.But it wasn't until January of this year that McGraw Hill sent the book to press. Goldstein and Dillon quickly handled the proofreading. Because he lived in Pittsburgh and she in Alexandria, they conferred by telephone about corrections to the manuscript. They ran up a $2,000 phone bill, and one Sunday they stayed on the phone for 16 hours.

Now, "At Dawn We Slept" is in bookstores throughout the country on the eve of the 40th anniversay of the attack on Pearl Harbor. Newspapers from New York to Los Angeles are featuring and television talkshows are beckoning, and there are many indications that Gordon Prange's obsession may soon be regarded as an historical classic.

Although Gordon Prange had no hand in the abridgement, it was his genius and an illness-forced compromise that is giving his life's work the recognition it deserves. Henry David Thoreau once observed that life makes most of us compromise. "The youth gets together his materials to build a bridge to the moon . . . and, at length, the middle-aged man concludes to build a woodshed with them."

That wasn't Gordon Prange. If he were alive he'd be busy on the bridge today. But we wouldn't have "At Dawn We Slept."