Baseball entered the second half of its season yesterday with a pleasant whiff of goofy dust on the wind.

That is to say, the New York Yankees issued an announcement.

The World Champions, as usual in their hour of distress, beat the sea with rods.

Henceforward, the Yanks informed a breathless world. Thurman Munson will be an outfielder, rookie Mike Heath will catch and Gary Thomasson will inherit the center field job of Mantle and DiMaggio.

As an addendum, the Yanks confirmed that Reggie Jackson would inherit the bench - becoming a part-time designated hitter against right-handed pitchers only.

Thus did the Yankees demonstrate how in baseball the utterly unthinkable can be transformed routinely into reality overnight. Especially when you are 11 1/2 games out of first place.

The Yanks also announced that Don Gullett, recently rejuvenated, could not lift his arm and that shortstop Bucky Dent was becoming the ninth Yank to join the disabled list.

These developments might move another owner to open a short suicide note.

Instead, the Yank's George Steinbrenner lectured his assembled outpatients, saying, "I am not going to lie down and die like a dog, and neither are you."

"There's going to be some changes made . . . discipline will be restored . . . rules will be enforced."

Rarely has football temperament and baseball reality collided so splendidly.

The inflexible rule of baseball is instability and insecurity, the whim of injury; the inescapable cycle of slump and streak.

Under Steinbrenner, once an assistant football coach at Purdue, the Yankees have tried to apply football theories to baseball.

The stock piling of talent, the three-deep depth chart to guard against any misfortune, the faith in discipline and organization have all failed in the face of Gullett's shoulder muscles, Ed Figueroa's elbow, Catfish Hunter's age.

The entire '78 season has borne testimony to baseball's intrinsic and elegant unpredictability - its unfairness, if you will.

Titillation is the essance of the long season. When will the bad break come? When will the rookie stop hitting/ When will the team chemistry of June dissolve under August heat and September pressure.

Yesterday's Yankee pronouncements sounded like the death rattle of the old champion. If so, then it was an appropriate clearing of the decks so new business might come under consideration.

"The lineup card has become a confrontation of egos between George (Steinbrenner) and (manager) Billy (Martin)," Roy White, a 15-year Yankee said last week. "You can't get a clear explanation of why you're playing or why you're benched."

The Yanks insist they'll never print the names of players on the backs of their pinsripe uniforms - too tacky. But, in effect, they already have.

"You're either George's boy or Billy's boy," laughed White, who is one of Billy's. "I'm convinced I was benched because I was playing too well and showing up George.

"We laugh about it . . . kid each other about how George has got (Lou) Piniella playing and me benched, or how Billy has benched Reggie to show his defiance.

"We're just guessing about this . . . that's the sad part. But it seems like they trade off - Billy gets to play so many of his favorites if George gets his way on other positions.

"It'd be funny if it wasn't so sick."

The Billy's boys vs. George's boys squabbling may have extended as far as the All-Star game. Munson said he wouldn't play, although he caught the final Yankee game before the All-Star break. Graig Nettles said he could play, then he couldn't, then he did. At the last minute, Jackson said he had a fever, and an eye doctor appointment, and . . . oh, well, a whole bunch of things to do.

Who could entangle this one-up manship? Probably not even the Yanks. The final result? Not one Yankee came to bat in the All-Star game, although they are defending World Champs and the manager of the ALs team was their manager.

White has been trying to get himself traded since last September.

"You'll see a lot of players traded after this season," White predicted. "Sparky Lyle, Mickey Rivers, Cliff Jackson, Jim Spencer, me . . . It can't stay this way with two qualified players for every position."

The irony thus far this season is that a World Championship team with at least 16 men capable of playing regularly still had fallen almost hopelessly out of contention by the All-Star break.

Meanwhile, teams near or under .500 like Kansas City, Texas, Oakland, Minnesota, Chicago (Cubs) and Pittsburgh are within sniffing distance of first place.

As the Yankees go kicking and hiting over the horizon, the new breed of baseball contenders comes into focus in the foreground.

Are the Boston Red Sox a great team, or will aging pitchers Luis Tiant and Bill Lee come unglued before October?

Have the Philadelphia Phillies, the winners of 203 games the last two years, lost their self-confidence as young pitchers Randy Lerch (4-6) and Larry Christenson (5-8) have become erratic?

What of the Kansas City Royals, the team that twice came within one inning of reaching the World Series? The spit of the pennant race begins its slow turning, the contenders feeling the gradually increasing heat as they are basted on all sides.

Of baseball's 26 teams, 15 remain fewer than 10 games from the league lead. Still time in a year marked by zaniness.

The party is just revving up. Only the hosts from New York, who though they would be the last to leave, seem to have departed. You can hear them arguing on their way to the car as they go.