In the American League East, baseball's best and deepest division, the law of pitching is immutable. Those who have it shall win and those who haven't shan't. That's why, when they think about their playoff chances, New York and Baltimore only have eyes for each other, while Milwaukee and Detroit, unless they have spectacular and unexpected improvement in starting pitching, will have to be satisfied to eye third place.

All current discussion of the Yankees -- Eric Soderholm's surgery, Reggie Jackson's pulled muscle, Dave Winfield's slow spring hitting, owner George Steinbrenner's deadline-beating trade to swap (in essence) Ruppert Jones for Jerry Mumphrey in center -- may be missing the point. The Yanks are built on pitching, and neither New York's fabulous strength (its bullpen) nor its worrisome weakness (lack of starting depth) has, as yet, changed an iota.

New York's offensive production (second in baseball) should change little.The improvements from Winfield should merely shore up for the loss of Soderholm, plus the vastly above-expectation years of Jim Spencer, Oscar Gamble and Bobby Murcer who, in 750 at-bats in '80, had 40 homers and 150 RBI. The Yanks would take last year's 820 runs right now and call it a good deal.

Overlooked in the Yankee shuffle may be that the impatient Steinbrenner has given up on Jones too soon. Just one spring ago, Jones arrived with these stats: 21 homers, 33 steals, 109 runs scored. Now, he, plus two significant pieces of the Yankee future -- Joe Lefebvre and Tim Lollar -- have gone to San Diego for Mumphrey who, despite a .298 average and 52 steals, had only a pretty good on-base percentage (.355) and an invisible slugging average (.372).

New York's fate rests more on the arms of third, fourth, fifth starters Ruby May, Tom Underwood and who knows than on Winfield's bat.

The Yanks still have no solid fifth starter and no bona fide right-handed starter, like Don Sutton, the free agent who got away. The pitching hand the Yankees hold at present, despite the best five-deep bullpen imaginable, isn't good enough to hold off Balitmore.

You can't have too much pitching, but the Orioles are trying. Throw out Steve Stone and Scott McGregor, who won't win 45 between them again but might get close to 40. You still have a rotation that includes Jim Palmer, who is temporarily healthy and resigned to getting late-inning relief help in his dotage; Mike Flanagan, whose shoulder is rehabilitated and will probably win 20; and healthy Dennis Martinez, who has an improved attitude and pitched excellently in winter ball. In addition, Sammy Stewart may be the most valuable insurance policy and all-purpose pitcher (spot starter, long and short reliever) in the AL.

After four straight miserable April starts, the O's, for the moment, have plenty of good news from Florida. The starters, except for perennial late-bird Stone, look sharp and the key comeback hitter, Doug DeCinces, looks a bit like the terror of second-half '78.

The O's only headache so far has been Manager Earl Weaver, who has caused concern throughout the Oriole organization at his sutbborn insistence on aggravating umpires to the point where he may seriously alienate their affections. Some think, nay, hope, that Weaver is merely trying to build a fire under his slow-starting club, or that his ejections and three-day suspension in Florida were just his way of stealing headlines from the Yankees, in whose shadow he hates to feel his team is dwelling.

A darker possibility is that Weaver has passed the stage where he can tolerate abuse or curses from callow young umpires who think they can treat him as if he were some nuisance that they, with their new union security, can gang up on and badger into submission. If his short fuse this spring is motivated by strategy, it may work; if it is simply cantankerousness -- a blind spot in an otherwise subtle mind -- then, as in the past, his umpire baiting may cost his team games.

The Brewers and Tigers have far worse problems than a manager with a rulebook complex. The bodacious Brewers will hit their 200 homers again and Rollie Fingers, even at 35, should be worth a 10-game improvement by himself. However, Milwaukee has a hidden problem: the soft underbelly of pitching is defense and the Brewers, after their trading binge, have, almost incredibly, risked weakening their good defense at five of eight positions. The quintet of Ted Simmons (catcher), Roy Howell (third), Jim Gantner (second), Paul Molitor (center) and Gorman Thomas (right) should not approach the glovework supplied by last year's inhabitants.

In starting pitching, Milwaukee and Detroit are mirror images. Each has modest aces -- Milwaukee's Moose Haas (16-15) and Mike Caldwell (13-11) matching Detroit's Jack Morris (16-15) and Milt Wilcox (13-11). Beyond that Milwaukee has blithe-spirited underachiever Pete Vuckovich (12-9 in St. Louis), Jim Slaton (shoulder surgery) and a collection of prayer rugs. Detroit has Dan Schatzeder (11-13), Dan Petry (10-9) and slim hopes.

The entire AL West depends on the status of four mystery pitching staffs in Kansas City, California, Texas and Oakland.

If the Royals can get solid, healthy years from their familiar rotation of Leonard-Gura-Splittorff-Gale and a reasonable facsimile of Dan Quisenberry's splendid 45 win-save season, then they win in the West because they have the best nine-man lineup in the league. Nobody can match the Royals for speed, defense, youth with experience and ability to play well on all surfaces and in parks of all shapes.

If the Royals, who may have the least depth of any contender in baseball, have inguries, then the West could be wild indeed.

The Angels field a heavenly lineup with Carew, Burleson, Lynn, Baylor, Ford, Downing (DH), Grich, Ed Ott (catcher) and Hobson that could exceed the 866 runs (most since '62) produced by the '79 bunch. If the Angels could assemble a respectable major league rotation, they might make up 31 games in the standings on K.C.

However, the Angels, despite all their greedy mound purchases, still look flimsy at best. The best of the bad lot are free agents Geoff Zahn (14-18) and Bill Travers (12-6), and tradee Ken Forsch (11-10), a good steal. The rest are outpatients from the sore arm clinic.

All the exiled ex-Red Sox on this team should feel right at home. They have gone from the club with the second-least enthusiatic attitude in the league to the team which, last season, set a new standard for most months played at waltz tempo.

The Angels' antithesis, the hellbent A's, were the league's simplest team in '80. Billy Martin had the best outfield in baseball, the best starting pitching and the worst everything else.

Now the A's are an example of the flash-in-the-pan team that must prove it isn't in the same category as the '76-'78 White Sox, who went from 64 wins to 90 then back to 71 when their "great young starters" proved only to be good. On Oakland's side is the fact that its 29-win improvement was built on rock, not sand. The A's had an astronomical improvement of 331 runs in differential, going from being outscored by 287 runs in '79 to outscoring their foes by 44 last year.

This is the season when pundits have ginally gotten tired of touting Texas. Thrice burned, finally shy, the Rangers still have as their stoppers the over-rated duo of Jon Matlack (37-42 the last four years) and Doc Medich (no 15-win season in five years). Still, Texas could improve 10 or more games on its 85-loss debacle of '80 if spaceman Jim Kern, gone from phenomenal to flop, can be a decent fireman, freeing Danny Darwin to start.

One of the year's best bets for a 10-game improvement are the White Sox who, by gathering Ron LeFlore, Carlton Fisk and Greg Luzinski for cash, may have boosted their offense from the worst in baseball is merely bad. Anyone with a self-destructive complusion to bet on fifth-place-to-first-place miracles should probably consider the potential in the three-way parlay between Chicago Manager Tony LaRussa's brain, Fisk's ability to handle pitchers and the live left arms on the White Sox staff.