WAITING for Derek Jeter upon his clubhouse arrival yesterday morning were three of his posters hung by pranking Yankee teammates to mock the shortstop.

It was Derek Jeter Growth Chart Day, so these 6-foot-3 photos were arrayed for his embarrassment. One in the trainer’s room. One in the middle of the clubhouse. One defaced with a painted-on mustache, blacked-out teeth and scrawled jibes draped like a door to his locker.

But the true Derek Jeter Growth Chart had been unfurled the previous evening, when the Yankee shortstop showed exactly what he has blossomed into. On a Friday night of chill and misty rain that was knocking down balls in the air, Jeter obliterated a scoreless tie in the fifth inning with a three-run homer well beyond the 408-foot sign in center.

Ken Griffey took a few defeatist lopes toward the wall with his back to the infield. Alex Rodriguez, Jeter’s best friend in baseball, jumped up from Seattle’s bench to examine and admire the flight. Those two represented the individuals in the ballpark that would have been voted most likely to be able to deliver such a mighty blow in adverse conditions.

Even a year ago, Jeter explained he would not have been a candidate. He said he would probably have used an inside-out swing on the Makoto Suzuki hanging splitter and accepted an RBI single to right. But another off-season of intense weightlifting and sweaty drills with minor-league roving hitting coach Gary Denbo on the art of using his top hand more to drive pitches has changed all that.

Now, more than ever, he can break a game open with his might. He may remain New York’s most eligible single man, but he is no singles man any more. He has six homers, four triples and nine doubles – the 19 extra-base hits ranking him among the AL’s top five. So does his .376 average.

“He’s improved at a rate that no one could fathom,” Paul O’Neill said. “He is now one of those guys that makes everyone stop and watch his batting practice. He can drive a ball out to all fields. He is embarrassing the rest of us.”

Jeter could do nothing in yesterday’s game to save the Yankees. Orlando Hernandez allowed six straight Mariners to reach and score with two out in the fifth, as he put together his second poor start in a row and his third in his last five.

Seattle won 14-5 and one of few Yankee highlights was that Jeter singled in the third to reach base by hit or walk now in all 29 Yankee games. That matches Dave Winfield (1988) for the longest such streak to open a Yankee season in the past quarter century.

That provides nice symmetry since Winfield was Jeter’s favorite player growing up. But back then, spending his summers with his grandparents in New Jersey, Jeter was a reedy kid with bigger dreams than muscles.

“He has earned his strength the hard way,” David Cone said. ‘Instead of hanging around New York and making a ton in endorsements, he goes down to Tampa during the winter and goes to work. He keeps getting better and better and that is a direct result of his off-season program.”

Jeter does not want to become beholden to the home run. He thinks he did that late last year in an attempt to reach 20 and had his entire offense suffer because of it. Jeter wants the results in extra-base hits. His career-highs are 31 doubles, 8 triples and 19 homers. Just to give an idea of how good Jeter has been through 29 games in 1999, he projects to 50 doubles, 22 triples and 34 homers.

“I think the MVP talk about him is very well deserved,” said Rodriguez, currently out for Seattle with a knee injury.

“He’s taken his game to another whole level. Pitchers used to be able to pound him in, pound him in and pound him in. Now, he’ll hit that flare to right field or hurt you deep like [Friday]. He stuck a knife in our heart.”

Cone called the ball Jeter hit Friday one of the hardest he’s ever seen at the Stadium.

Chili Davis said “I thought it was in the black because he just hit the mess out of it. He can do that now.”

Don Zimmer said, “you don’t hit balls in Yankee Stadium that you just know are over the center-field fence off the bat. But when he hit that ball, you just knew.”

Said Jeter, “Any time you put in the hard work and see results it is gratifying.”

For Jeter, that is about as big a self-compliment as he is capable of. But maybe he is just waiting. Maybe he senses what we all do. That there is a lot more to come. That no growth chart can truly hold him.