The last ballplayer left in emerald Al Lang Stadium was the highest-paid man in baseball, George Foster of the New York Mets.

As the remaining rivulets of a modest crowd were draining down the ramps, Foster seemed like an identityless speck as he stood beneath the left field foul pole. Foster always looks inconspicuous and camouflaged, except for those brief moments when his black bat temporarily liberates baseballs from gravity.

"Foster's like Larry Hisle was for me in Milwaukee," says new Mets Manager George Bamberger. "He isn't a leader by yelling, or even talking. He's a leader by home runs."

Only the children noticed Foster. By ones and twos, until they were dozens, the small ones escaped their parental units and invaded the outfield where he was methodically running the track from pole to pole as the sun went down.

"Running now," said Foster succinctly. "Form a line behind my glove."

And they did. Foster running with mincing strides. The children standing patiently in a line so straight no school teacher could ever duplicate it.

"You always dream about trading for the pluperfect player. But you can't, because if an excellent player isn't scarred in some way, you don't get a chance to trade for them," said Mets General Manager Frank Cashen, ticking off the supposedly damaged-goods sluggers he had grabbed over the years--Frank Robinson, Lee May, Ken Singleton in Baltimore and, now, with the Mets, Dave Kingman and Ellis Valentine. Then Cashen had second thoughts. "The exception," he said, "is George Foster."

Finally, Foster, standing with feet shoulder-width apart, weight evenly distributed, shoulders back, stomach in, began signing autographs.

A nervous little boy wanted a snapshot. "Step back," murmured Foster, making sure he was exactly the proper distance away. "Keep your fingers off the lens."

Click.

Foster, as he continued signing, made the boy wait until the pop-out film had developed, so he could be sure the photo was acceptable. You don't send a child way with an out-of-focus hero.

Gradually, high schoolers and adults joined the line of kids. "Kingman gets out of here by the fifth inning," said one lad almost as big as the 6-foot-1, 195-pound Foster. "Yeah," answered his buddy. "Foster's just a good guy."

When they got to Foster, the braver one said, "Wanna trade caps?"

Foster's eyes came up slowly. He smiled slightly. "Don't think so," he said. Small laugh all around. End of banter.

A small Dennis the Menace--a devil's seed in cherub's clothing--wandered up to Foster's side.

"No breaking line," said Foster.

The insolent child stood there for minutes, piece of paper expectantly, demandingly outstretched. Foster ignored him as one might a dog begging for table scraps. Thus was chaos defeated.

"I suppose the most pleasant thing this spring has been the attitude Foster has brought with him," says the rumpled little Cashen, who looks like the George Smiley of GMs as he sits in the general admission seats in a floppy hat, totally unnoticed, in the midst of a mob of Mets fans.

"He has the attitude that he's going to help us rebuild this club, help us sell tickets. He's acted like I'd written the script . . . When I got here (two years ago this month) the Mets were a whipping boy. In New York, we're too often looked on like a buffoon. When you start three stories down, it takes a while to get to ground level. But, with Foster and Kingman and Valentine, we've built a power base."

The autograph line has ended, but, now, a half-dozen adults remain.

One middle-aged man asks, "Can I take your picture ?"

Foster, as if he were still correcting one of the children, says, " 'Can' means, 'Do I have the ability?' "

"I mean 'May I?' " answers the man, accepting the rebuff like a compliment.

Slowly and timidly, the fans begin to ask questions. Kingman won't give interviews to the press. Foster gives full-scale interviews to fans. If they, like the children, remain orderly and deferential.

Why does he take so infernally long in the batter's box? Is it to intimidate the pitchers?

"Concentration is the bridge between the physical and the mental," says Foster, who adores pithy phrases and parables, almost as much as he likes the major league-leading 671 RBI he has in the last six years. "Between pitches there's a breakage. I have to visualize the pitcher's release point all over again. Sometimes I can. But when I can't, I don't step in until I can."

Don't pitchers get mad at his procrastination and throw at him?

"A hitter who is ball shy literally has two strikes against him. I believe that my faith gives me a spiritual or divine protection. I've been hit, but not hurt. I believe that though I may be hit, I'm not going to be penetrated. You believe that no matter how close, you'll get away," says Foster, brushing his own face, as though with a fast ball. "Once, Nolan Ryan threw a fast ball that, I'm told, went right by my head. I never saw it until it hit the backstop. I feel it's divine protection."

Will he, as a shy person, enjoy the public role of leading the Mets' publicity counter-blitz against the entrenched Yankees?

"I'm looking forward to it," he says. "It's not that I couldn't do it (be a drawing card) in Cincinnati. It's that I didn't get the chance. There, I wasn't asked. Here, they're asking me to do it and I appreciate it."

What does a $12-million contract (for six years), and New York-style media exposure, mean to him?

The answer is a surprise, except to those who have known the almost antimaterialistic, antisensual Foster for years. After all, this is a 33-year-old man who has never smoked, drunk liquor, taken drugs, chewed anything, or, until he was past 30, even bothered to own a car. Foster thinks a vice is a tool found in the basement.

"George might be the cleanest liver in New York City," says Bamberger.

"I plan to live in Long Island or Connecticut," responds Foster, wryly.

What does his new wealth and fame bring to mind?

"It should help the George Foster Home in Dayton, Ohio," he says. "It's a (foster) home for boys 13 to 17 who have gotten in trouble and need a second or third chance."

Foster helped found the home four years ago, when he was a long way from being a millionaire, but never mentioned it to anybody in the media.

"The home is only located 50 miles from Cincinnati, but it's just now getting some attention since I came to New York," he says pointedly. "It is dependent upon private contributions."

So, if the foster home is his first thought, what is his second money-related project?

"A home for girls," he says. "But we don't want to branch off too soon."

One man and his adult son bid their stunned farewells to this superstar who has talked to them more than all the other "celebrities" in their lifetimes.

"Good luck," says the father.

"Best wishes," says the son.

Foster approaches the father, teasingly puts his arms conspiratorially around his shoulder and says, "I liked what your son said better--'Best wishes.' You know, there really isn't any such thing as 'good luck,' because luck only comes to those who are prepared."