One of the nicest aspects of baseball is the near certainty that it will make a fool of anyone who tires to predict it.

The first half of the American League season is a clear case in point.

Baseball is excellently suited for analysis, as long as we confine ourselves to the past, the present or even the long-range future.

It's no mystery to explain, in great statistical detail, what happened last season.Nor is it tough to figure out why a team is currently hot or cold. We can even look with considerable assurance at thelong-term prospects of a team or player and say, "the Yankees are well set for the next five years," or "Paul Molitor will be a star for the next decade."

However, the one sliceof time that always interests us most is the one we can never get even the slipperiest grip on. What's going to happento the short-term future: next week, next month and for therest of this season? That is a miasma of foul vapors and deceits.

And, of course, that is a primary reason why a sport that seems so eminently comprehensible can hold our attention, year after year.

An ideal illustration of baseball's capacity for fine sleight-of-hand, quick shell-game reversal of expectations, is the defending American League champion Baltimore Orioles.

The Bird shock is not their 40-33 record. Plenty of defending titlists stumble for half a year. The stunner is the almost total unpredictability of why the O's are eight games behind New York and worried.

In March, Baltimore had a shopping list of sensible concerns. Almost all those frets have worked themselves out.

Eddie Murray forgot us his World Series nightmare and has 49 RBI. The deep-depth bench of Ayala, Crowley, Kelly and Lowenstein is better than ever with 100 runs produced, a dozen homers and a .297 average in its first 296 at-bats. Jim Palmer (8-4) has been solid, while the club's Nos. 4 and 5 startersof 1979 -- Scott McGregor and Steve Stone -- have a comined 19-6 record.

Had Earl Weaver been told all this -- alongwith Al Bumbry's .330 average and the news that the O's would be the Eastern Division's most injury-free team -- the manager would probably have assumed his Birds would now be 8 games ahead, not 8 behind.

If Weaver had also been given apeek at the Al's disabled list for the first three months -- littered with star names from New York, Milwaukee and Boston like Jackson, Jones, Gamble, Molitor, Rice and Fisk -- hemight have drooled.

Perhaps only in baseball, of the major sports, can such remarkably unexpected results be produced by such subtle and hair's-breadth causes.

In pro football and basketball for instance, a player's form varies little from year to year. A tiny bone chip in the wrist doesn't disable Mean Joe Greene for months as it did AL MVP Don Baylor. A sore arm -- not broken, just sore -- doesn't turn Julius Erving from a star to a bum the way a baseball pitcher like Texas' fireman-of-the-year, Jim Kern, can go from glory to a 2-9 record because of injuries he doesn't even notice until he throws a ball.

The big surprise in both AL divisions is not Who is far in front -- rebounding powers in Kansas City and New York -- but why they are back on top. Even those teams' rookie managers -- Jim Frey and Dick Howser -- are stunned.

"Everything about this season has been a total surprise," Frey said. "I figured the heart of this team was my No. 3-4-5-6 hitters -- Brett, Otis, Porter andMcRae. I thought I'd write those four names down every day.

"Well, all four of them have been on the DL. They've been on the field together exactly twice in 74 games," Frey said yesterday, his team leading the West by eight games.

The Royals' pitching staff (21st in ERA in '79) has been salvaged, basically, by one man -- Larry Gura, who has a 10-3 record, 2.23 ERA and 137 innings pitched. Was it Frey's planto make Gura a complete-game stopper?

"Hell, no." Frey said, "I can't explain it. He just started going nine innings every time out."

Howser is just as perplexed, and just as pleased.

"The more we get injured, the better we play.It's ridiculous. We're carrying it too far," he said, thinking back to last Saturday when his team won, 11-10, in the ninth with a lineup minus Reggie Jackson, Ruppert Jones, Oscar Gamble, Bucky Dent and Graig Nettles.

Howser has had to resort to a third-string shortstop (Dennis Sherrill), a third-string catcher (Dennis Werth), and two rookie outfielders as regulars (Joe Lefebyre and Bobby Brown.)

Farm-system depth is nice, and the Yanks have it. But luck also helps and the Yanks have had buckets full.

Last year, the Yanks were 10th in the AL in runs scored, so, Howser decided, "I'dencourage some of my hitters, especially the left-handers, to think about the long ball a little more."

At the moment, New York has 100 homers in 72 games -- a 225-homer pace that would be the second-highest in history. Nobody expected it, could have predicted it or has the slightest ideas if itcan continue for another three months.

Why is baseball so full of mutations and aberrations: the sport full of sports?

How can K.C.'s Clint Hurdle go from hitting .236 at Omaha to batting .331 in the majors?

How can Oakland suddenly develop a class outfield -- set for the '80s, it seems --of Tony Armas (14 homers), Dwayne Murphy (.313) and Rickey Henderson (33 steals), none of whom even have photos next totheir names in "Who's Who in Baseball ('80)"?

How can Steve Stone, career record 78-79 before this year, be tied forthe lead in wins (11-3) and perhaps get the startng assignment in the All-star Game next week?

How can one organization develop six promising starting pitchers -- all left-handed -- at the same time, as the Chicago White Sox have done on their rise to second place in the West?

How can the Tigers trade a superstar, Ron LeFlore, for the one young pitcher in all of baseball that they were most certain would be a winner -- Dan Schatzeder, and then have Schatzeder arrive atthe All-Star break with the worst ERA of any regularly usedpitcher in baseball?

The reason may be that the differences between the great mass of ballplayers is much small thanin other sports. The world produces a limited number of 6-foot-9 power forwards and 250-pound pulling guards. But thewoods are full of 6-foot, 180-pound quality athletes.

Ina game where skills, polished over the years, are as important as raw talent and where mind and morale will frequently wear down mere muscle over 162 games, the margins of successand failure are thinner than most baseball fans like to believe.

The teams in which great affection are invested alltread on a sort of thin ice. Bad teams cannot become great, but they can "play over their heads" far longer in baseball than in any other sport. Conversely, fine teams teams canfind mysterious ways to lose for months on end.

The moral is as entertaining as any fan could hope. In other sports, the league standing seem cast in bronze. The Pittsburgh Steelers and Dallas Cowboys just won't go away, once entrenched. Whoever has Kareem Abdul-Jabbar will have to work hard to lose.

But in baseball every crown rests uneasy.

Fortunes shift suddenly and inexplicably. Ask the Boston Red Sox about their 14-game lead in July 1978. Sudden change -- the exhilaration of a long winning streak to the teamwide nausea of the big slump -- is the rule for almost every baseball season, not the exception.

Only in retrospect does themadness make some sense. Baseballs are never made of crystal.