BEING a baseball fan used to be a piece of cake. Winter was The Sporting News and the Hot Stove League, spring was newspaper stories out of the training camps, summer was ball games and box scores, fall was the World Series and post-Series depression; a fan could handle all this with one hand and still have the other free for the irritating necessities of life. But now everything has changed. Thanks to a number of bright, rather obsessive fellows, the best known of whom is Bill James, being a fan has become a fulltime job; not merely are there games to be watched, stories to be read and batting averages to be pondered, but one must also come to grips with a bewildering variety of statistics, charts and judgments produced by the new science called "sabermetrics."

This arcane study, which takes its name from a youthful organization called the Society for American Baseball Research (SABR), is defined by James as "the search for objective knowledge about baseball." It is a search that James has conducted since 1977 in an annual paperback first called The Baseball Abstract, when James published it himself, and now published by Ballantine as The Bill James Baseball Abstract: a compendium of numbers and words in which James seeks, through various elaborate formulae, to determine how good each major-league ballplayer really is. It's a mixture of "fact" (statistics) and opinion that can be read by both the casual fan and the terminal nut, since James writes a lively, colloquial prose and since it is not necessary to comprehend his mathematical exercises in order to appreciate the judgments he draws from them.

Over the past several years the Abstract has become popular among fans, hard-core and otherwise, and James has become something of an industry; not merely does he do the Abstract, he also publishes a newsletter and hires himself out as an expert counsel in baseball salary negotiations. Now, perhaps inevitably, his long hand has reached into the mists of baseball history and come forth with The Bill James Historical Baseball Abstract, his magnum opus. It is a fat, juicy production that can be read straight through -- an exhausting enterprise, I assure you -- or nibbled away at like a bag of peanuts or box of Cracker Jacks; either way it is great fun, and its many fiercely argued opinions are sure to give your blood pressure a good workout.

The book is divided into three sections: a decade-by-decade history of baseball from 1870 to 1979, an assessment and comparison of the great and near-great players at each position, and a listing of detailed statistics for some 200 notable players. To the fan for whom sabermetrics is a riddle wrapped in a mystery inside an enigma, the first two sections offer the greatest pleasures; to the sabermetrician no doubt the third will be Elysium, but that is a question sabermetricians will have to settle among themselves, I being incompetent to pass judgment.

In the first section, James makes a serious effort to write history from the ground up: grass-roots history, as it is often called in the academic departments. He concentrates less on each decade's most celebrated players, games and controversies than on the more mundane details that help give today's reader a feel for what the game was actually like. He traces the evolution of ballparks and equipment, the constantly shifting ethnic and racial nature of the game's population, the belated expansion of the major leagues out of the Northeast and Midwest. For each decade he produces a box that contains information, trivial and otherwise, and opinions, often arbitrary but almost always amusing. He pauses, too, for digressions into such matters as the slow recognition of the no-hitter as a significant event, the selection process for the Hall of Fame (he's against it, with good reason) and the development of relief pitching as a specialized craft. He rescues many players from undeserving oblivion, deflates a few exaggerated reputations, and generally has himself a high old time of it.

It's in the second section, though, that James really gets into gear. He makes a habit, here as in the annual Abstracts, of pooh-poohing player ratings and comparisons, but he obviously delights in them. He takes them seriously, too, as is evident in the central question he asks about every player: "What did he do to help his teams win?" The casual fan may get swept away by a player's individual statistics and spectacular exploits, but James always has his eye on the only business that really counts: the contributions the player makes to what is, after all, first and foremost a team game. His statistics play a big role in the judgments he reaches, needless to say, but he is quick to point out that statistics cannot provide final answers and that other considerations must enter the equation, chief among them perhaps the conditions of the time and place in which each man actually played; as he observes at one point, "One of the major goals of this book, as you have likely noticed, has been to distinguish accurately between that which was written and said about the player's skills while he was active, and that which came along later."

JAMES rates players in two categories: their effectiveness over the full length of their careers and their effectiveness at peak performance. He lists no ultimate all-star team, but by taking his career-performance rankings position-by- position the reader can assemble one: Yogi Berra at catcher, Lou Gehrig at first base, Eddie Collins at second, Mike Schmidt at third, Honus Wagner at shortstop, Stan Musial in left field, Ty Cobb in center, Babe Ruth in right, Walter Johnson as righthanded pitcher and Lefty Grove as southpaw. His peak-performance team is remarkably similar: the only substitutions are Roy Campanella at catcher, Joe Morgan at second and Mickey Mantle in center. But he also offers his list of the 100 greatest players, irrespective of position, and see how things change: the first 10, for career performance, are Babe Ruth, Honus Wagner, Lefty Grove, Stan Musial, Henry Aaron, Ty Cobb, Lou Gehrig, Joe Dimaggio, Willie Mays and Ted Williams. That's a crowded outfield, folks.

It's a crowded book as well, yet each reader is likely to feel it's not crowded enough. I wish there were more discussion of the Negro Leagues, and I wonder why James didn't pause during his history of the 1950s to write about the 1954 Cleveland Indians, a great team that has been denied full acknowledgement of its greatness because of Willie Mays' epic catch and Dusty Rhodes' pop-fly homers. There are some startling omissions in the lists of "best baseball books" for each decade, notably Harold Seymour's two-volume history of the game and Bill Veeck's Veeck As in Wreck, and excessive praise is given to a number of books that do not deserve it. But the book's most grievous flaw, this one clearly no question of subjective judgment, is a wholly inadequate index that ignores many names mentioned in the text (Ken Singleton, twice mentioned, is nowhere in the index) and is sometimes simply inaccurate: the "evaluation" of Cap Anson, listed in the index as pages 33-35, turns out to be an evaluation of Buck Ewing in which Anson is cited only casually. An index is of crucial importance in a book such as this, in which readers tend to flip about from subject to subject, and in future editions James owes his readers a better one.

But this shortcoming, though serious, does not diminish the many pleasures offered by this doorstopper of a book. Far more than the annual Abstracts, it is accessible to the reader who likes baseball, is interested in its players and history, but understands that the game is not the only stop on life's railroad. My own shelf of genuinely first-rate baseball books is very small, but a place will have to be found on it for this one.