THERE ARE two landmark Chappaqua, N.Y. One is Horace "Go West, young Man Greeley, who was somehow set up by the townsfolk with his arm pointing to the East.

The other is the cornerstone from the old Yankee Stadium, which sits half-buried at the foot of Bert Randolph Sugar's driveway.

When Sugar was a youngster, he sold the bulldog edition of The Washington Post outside Griffith Stadium, keeping the last three papers under his arm and duck-walking past the ticket-takers who didn't know he was gate-crashing.

Today, at 37, Sugar has his house so filled with baseball memorabilia that even Cooperstown in envious.

When Yankee Stadium closed for refurbishing, Sugar figured the pickings might be good and got permission to collect material that was to be discarded. He not only got the cornerstone, but also he original mold for the Lou Gehrig centerfield monument, a Babe Ruth contract and genuine $300,000 stock certificates from the 1915 purchase of the team by Jake Rupert. He already had Jimmy Foxx's first baseman's glove, Ty Cobb's left shoe and Jim Thorpe's right shoe.

Sugar is a lawyer who just brought a landmark case before the Supreme Court, once edited Argosy, wrote a book on Houdini and organized a cross-country icentennial horse race.

He also finds time to get together and correspond with his peers among baseball buffs, members of the Society for American Baseball Research (SABR).

SABR is the national pastime's think tank, a sort of baseball Brookings Institution with the appropriate address of Box 323, Cooperstown, N.Y. 13326.

"So much is baseball is overlooked," said SABR stalwart Pete Simonelli, a New York-based oil executive. "The average person can't be completely aware of American hisoty without first knowing baseball's role in the culture."

SABR issues a monthly newsletter, organizes local conferences and publishes an annual journal filled with articles like "The Most Lopsided Shutouts" and "Moses Solomon: The Rabbi of Swat."

Who belongs to this dedicated group? Anything but your stereotyped beer-guzzling ballpart jocks:

Dick Cramer, an eminent Philadelphia chemist but more famous in baseball circles for the BRA formula, a statistic judged more accurate than the batting average for evaluating player effectiveness.

Steven Greyser, Harvard Business School professor and secretary of the Business Review, who lists his chief baseball interest as "might-have-been records" and who codirects a sports management seminar at Harvard.

Robert Kingsley, a retired mapper for the Defense Department, who now plots ballpark dimensions.

Steven Kotz, Berkeley law student, who has researched the "common law origins of the infield fly rule."

There are doctors and lawyers and at least one airline pilot, according to SABR president L. Robert Davis, a Washington resident who also edits the annual journal. Plus policemen, a dynamite blaster, a bartender, the controller of a Las Vegas nightclub, a diplomat in Rome, a Seattle rabbi, a priest in Janpan, a missionary, numerous sportswriters and editors and statisticians.

SABR's purpose is the study of baseball history and statistics, but each member lists specific interests: "minor leagues," "relief pitching," "baseball trades," "baseball in literature," "switch hitters," "umpires," and so on. In all, the 400 members listed 175 fields of interest in a recent directory.

One member complied a comprehensive index to every baseball statistic ever recorded. Another produced a list of every home run, day-by-day. Under way is a compilation of every inside-the-park home run.

When Dick Cramer told Philadelphia Phillies general manager Paul Owens that he should junk the batting average and try a new statistic to rate ballplayers, Owens wrote back, "Yeah, I think that's a nice idea."

So Cramer analyzed a few deals Owens had made, suggested several new ones, and sent a followup note to the Phils. He never got a response.

That kind of reaction from baseball's establishment is nothing new for Cramer, who adapts the complex techniques of his profession to the computer baseball hobby he pursues.

"We try to maximize the effects that we observe," he said of his chemical work. "This is accomplished by testing series of compounds which are structurally related."

It's that way in baseball too. "One experiment is to make lineups of one batter - nine Babe Ruths, for instance - and see how many runs such a team would score." By comparing this to a similar computer run of nine weak-hitting Sandy Koufaxes, Cramer can establish the normal limits of baseball play - "About 20 runs per game for the Ruths, one-third run a game for the pitchers."

Cramer's Batters Run Average is figured by multiplying a player's on-base average (his run-scoring ability) by his slugging percentage (his run-driving-in ability). With this formula, he predicts with remarkable accuracy the final standings each year.

"We always outpredict the magazines, he claimed, citing a coworker so successful wagering on baseball games with the BRA that his bookie refused to deal with him anymore.

Cramer is convinced his data could be of value to front office executives.

"General managers are always making trades when they don't really know the value of the players involved." He points to the Joe Morgan deal.

"Morgan has always been a terribly valuable player to his team, as compared to Lee May," he said. "Hitting home runs is a colorful thing to do, but May grounds into a lot of double plays, walks infrequently and is just a slightly-better-than-average hitter over his career.

Kingsley got so engrossed at Myrtle Beach in 1951 studying sports summaries in the Charlotte Observer he got sunburned. But he was undeterred. He spent the next 10 years studying every aspect of baseball performance he could think of - home runs, runs batted in, and so on. Except for ballparks.

So he spent several more years on stadium dimensions, fence heights and wind resistance. "I spent two years alone on eliminating the logical geophysical factors," he notes proudly.

He sends around an annual fact sheet comparing ballpark efficiency. He's been hired as consultant by stadium architects and established the fence lengths for Busch Stadium in St. Louis.

"The team complained that not enough home runs were being hit and the fences must have been set wrong," Kingsley snorted. "Nonsense! The Cardinals haven't had a decent ballplayer to hit one of there in years."

SABR has had its share of controversies, too.

David Neft put together MacMillan's 3,000-plus-page Baseball Encyclopedia in 1968.In the process, Neft discovered that Babe Ruth's lifetime home run total was incorrect. Instead of 714, the "Sultan of Swat" should have been crdited with 715.

Because Hank Aaron was rapidly approaching Ruth's total, this discovery was significant. Moreover, commissioner Bowie Kuhn was giving his official imprimateur to the book, so the numbers had to be right.

Apparently Ruth had hit a homer in 1926 in the bottom of the 10th inning with a man on base and the score tied. Under the rules then, as soon as the first runner scored the game ended. Ruth wasn't credited with a four-bagger.

Baseball rules were later changed and a ball gone is a ball gone and a homer.

Neft thought Ruth ought to be credited with an extra home run, to bring the statistics into line with today's baseball rules. The voice of moderation prevailed, however, as Clifford Kachline, baseball historian at the hall of Fame in Cooperstown, protested. The idea was dropped, the book published, and Ruth still has 714 homers.