In the fall of 1973 David Halberstam sat in the book-lined den of his Manhattan brownstone apartment, watching Watergate unfold on television and thinking about his next project. Nine years earlier, he had won the Pulitzer Prize for his Vietnam reporting, and at the moment his brilliant autopsy of the Kennedy and Johnson administrations, The Best and the Brightest, was a best-seller.

Halberstam considered doing a book on oil. "But oil really didn't interest me," he says. "Then the light switched on: There was Dan Rather going one-on-one with the President over Watergate. In Vietnam and Watergate, it was not the President v. Congress or the President v. the opposition party. It was the President v. the media. Who runs the media? I decided to find out."

After five years and 700 interviews, Halberstam, 45, offers his answer in The Powers That Be (Knopf, $15), a 771-page tome that peers into the newsrooms and boardrooms of four communications empires: the Washington Post, the Los Angeles Times, Time Inc. and CBS. Why these four? "CBS is simply the best network," explains the author. "The Washington Post was responsible for uncovering Watergate. TIME is the most powerful opinion-shaper among magazines. And the L.A. Times is more important than most people think: It invented Richard Nixon."

The book may well be, as his colleague Theodore H. White puts it, "far better than The Best and the Brightest—nothing less than the illumination of the past two decades." Still, it is Halberstam's style to paint his characters in black or white and neglect the grays. Thus, heroes and villains emerge as he builds the story of each communications colossus, piling anecdote on anecdote.

Halberstam is as fiercely loyal to his friends in and out of the press as he is unforgiving of enemies. "He may be the grandson of Polish Jews, but there is a lot of Sicilian in David," says Gay Talese, author of The Kingdom and the Power, who first met Halberstam in the New York Times newsroom 18 years ago. "We both remember people who were nice to us on the way up—and we never forget the others. We're great on grudges." Concurs another friend, Pulitzer Prize-winning humorist Russell Baker: "David is passionately moral—the last of the Old Testament prophets."

A weatherbeaten 6'3" and 195 lbs., he somewhat looks the part. Yet Halberstam is not the most famous crusader to come out of the small Connecticut town of Winsted; one of his schoolmates was a studious fellow named Ralph Nader. David, the son of a doctor and a second-grade teacher, was elected managing editor of the Harvard Crimson (while coming perilously close to flunking out).

After graduation in 1955, he headed south to chase fire engines for the tiny (circ. 4,000) West Point, Miss. Daily Times Leader. He quickly distinguished himself on the reporting staff; in fact, he was the reporting staff. Halberstam considers his subsequent four years covering civil rights for The Tennessean in Nashville "the happiest time of my life."

In 1961 James Reston lured him to the New York Times. First posted to Washington—"It was not really my kind of town; I didn't do well"—Halberstam later found covering war in the Congo more to his taste. "It was out of control, terribly chaotic," says Halberstam. "I've never been so scared."

Not even in Vietnam, which Halberstam is quick to downplay as a topic of conversation. "War correspondents tend to live in the past," he shrugs. "I don't want to become the national bore." As one of the earliest on-the-scene critics of Saigon's Diem regime (he arrived in 1962 and left to become the Times' Warsaw correspondent three years later), he earned the animosity of John Kennedy and Lyndon Johnson—as well as his Pulitzer. "What makes him a great reporter," observes Teddy White, "is his infectious enthusiasm. David salivates over a good story—he becomes incandescent!"

Halberstam quit the Times in 1967 to work on The Best and write magazine articles. Since the early '70s he has divided his time between New York and Nantucket, where he owns a house. He writes in the morning, indulging his passions for tennis and fishing in the afternoon. Halberstam's 10-year marriage to Polish actress Elzbieta Czyzewska ended in 1975, and after dating the likes of actress Hope Lange, he fell in love with former Times fashion reporter Jean Butler. They have lived together since 1977.

She accompanied him on a recent six-week tour of South Africa ("A real bloodbath is coming," he predicts). They will marry in June and honeymoon in Venice after he writes his African story for the Atlantic Monthly and completes a promotional tour for The Powers. "This is when I turn myself into a human cassette," he admits.

Meanwhile Halberstam ponders his next step. "I spent over a decade on two books," he says, "and I'm glad I did—I can honestly say I couldn't have done better. But it's finally time to take life in smaller bites."