Early in the New York Yankees' training camp last year, Manager Yogi Berra heard it from Himself, George Steinbrenner. "Someday, Lou Piniella will be manager of the Yankees," the supreme voice in Yankee affairs said to a baseball writer, and not off the record.

It was the sort of talk that could dismay a resident Yankee manager, this being told that Piniella was in the wings and already clothed with Steinbrenner's blessing. Were Steinbrenner of a Shakespearean bent, he could have couched it for Berra in other terms: "Beware thee, fellow, for, forsooth, there is a manager-in-waiting."

There was, indeed, and Piniella now is it. Oh, there was a small delay in bringing this about because Steinbrenner brought in an earlier love, Billy Martin, for a fourth romance with the job after firing Berra in May. But as usual, Steinbrenner and Martin split up again at the season's end. By Steinbrenner's lights, Martin had proved unfaithful by failing, by two games, to get the Yankees into the 1985 playoffs.

Steinbrenner, with the power to fulfill his own prophesy, quickly named Piniella for 1986. Recently in the Yankees' camp, new manager Piniella was saying, "I never was comfortable with what George said last year. I was Yogi's friend, and trying to mind my own business as batting coach. I told George I'd like the job, but only when my time comes."

Piniella represents approximately the dozenth managerial shift in the 14 years of Steinbrenner's ownership, which has established him as the all-time No. 1 switcher. In 1982, Steinbrenner surpassed himself with a triple switch -- three managers in one season.

Sitting in the manager's office, Piniella said, "I've been in this clubhouse 13 years and I've never been in this part of it. Sure, I know about the hectic history of Yankee managers. I know George is an involved club owner, but I want to win as much as he does."

He was reminded of Steinbrenner's fickle regard for Yankee managers, Piniella said, "by a friend who called me from Atlanta a couple of weeks ago and said, 'Lou, the Atlanta paper today has a headline about you and Steinbrenner. It says, 'Honeymoon Over.' Damn, we hadn't even opened up training camp and somebody wanted to make trouble."

The honeymoon clearly is over between Steinbrenner and Ken Griffey, whose demand for a trade prompted the following response from The Boss: "Who's going to take a 36-year-old outfielder with two gimpy knees making $960,000 a year besides me? Who else is that stupid?" Steinbrenner also advised Griffey to "shut up because I'm tired of him whining."

Steinbrenner has not yet expressed any displeasure with Piniella, a 6-foot-2, 42-year-old still-slim hunk of manhood who breaks into a smile easily, but only off the field. On it, there was always grim dedication.

"That's why I hired him," said Steinbrenner. "I like his determination and aggressiveness. I always thought he could be a leader. He was my hero that day in Fenway Park in 1978 in the playoffs when he fought the sun in right field and wouldn't give up on a hard hit. Stayed with it and held a runner at second base, saving the game and getting us into the World Series we won from the Dodgers. Sure, Lou is one of my heroes."

This year's spring training scene in Florida represents a giant leap for Piniella. Three miles north of the Yankees' camp where he is now the boss, Piniella was a rookie outfielder with the 1964 Washington Senators in Pompano Beach. They had drafted him from the Cleveland farm system.

In their 1964 camp, a Senators coach once described the rookie from Tampa with the shining black hair as "that pretty boy who's always in front of the mirror combing his ducktail haircut."

He was dismissed by the Senators as an inferior candidate for the majors. The Orioles looked at him for four games and returned him to the minors. Not until five years later did Kansas City give him much of a chance in the majors and he was traded to the Yankees five years later.

The pressure of managing the Yankees does not bother him, Piniella said.

"It's been pressure all my life," he said. "There's no more pressure than being a designated hitter; they expect a lot from you." In 1982 he was the American League's leading DH in batting average. He hit better in the majors than he did in the minors. And he hit better in the playoff and World Series games than he did in the regular season. You can look it up.

He may have rated as the most popular Yankee with Yankee Stadium fans in the post- Mantle-DiMaggio era. At his every appearance, the cheers of "Looooo" swept the place, leading one visiting stadium fan to mistake the sound and ask, "Why are they booing a nice guy like Piniella?"

On the Yankees, where he was close to all his teammates, there must be a new order of relationships, Piniella said. "You can't have the buddy system anymore. Friends but not buddies. The manager has too many tough decisions to make, and there has to be a separation."

He said he learned valuable lessons from Billy Martin while sitting on the Yankees' bench last season. "Billy taught me that you have to be aggressive all the time, that you vary your game and keep the other team guessing; that today's game is the most important one you'll ever play."

He'll have help this year in the Yankees' dugout, he said. "Joe Altobelli, from the Orioles, is an old friend and he'll be sitting with me. I can use his experience. Remember, Joe was manager of the year in 1983."

This season, Billy Martin and his sometimes loose tongue will be in the Yankees' television booth, but Piniella said he expects no mischief from that direction. He said Billy's an old friend and really a nicer guy than a lot of people think.