"Let's face it, I wanted to be a ballplayer," said Kenneth E. Moffett, the mediator, reminiscing about Ken Moffett, the lefty pitcher. "Couldn't break a pane of glass. You know what a guy said about me last year? Said my fast ball shoulda been arrested for loitering."

He cackles and sighs. "I went to all the tryout camps, the Phillies, the Cardinals, the Tigers. We'd all pile in a car and go. Once, Eddie Krajanck said, 'We'll be watching ya, kin.' He discovered (Robin) Roberts and (Curt) Simmons, I think. It was the most encouraging thing anyone ever said to me."

Contrary to published reports, free agent compensation is not the most intractable problem in the baseball negotiations. It is Ken Moffett's struggle to keep a straight face.

Moffett takes these things seriously, very seriously. It's just that "you better be able to laugh at yourself, and at the parties, too," he says.

Federal mediators are straight men. "Gotta wear my federal mediator's uniform," he says. Blue blazer, button-down shirt (preferable government issue white) and gray slacks.

Every day there are talks, Moffett descends from the 17th floor of the Doral Inn in New York, to face the cameras and the pens and explain why there is no baseball. Four hours before the strike was announced, Moffett said, "It's early yet. Nothing happens in this business until after dark."

He bared his fangs. "Like Dracula."

That's off the record. Federal mediators are not supposed to be glib.

Ray Grebey, the owners' chief negotiator, says, "He's a very low-key guy, he doesn't lose his cool."

Marvin Miller, the executive director of the Major League Baseball Players Association, says, "He tries to keep things as light as possible. Things tend to get grim up there. While these are serious matters, it doesn't help to get too grim."

Recently, a reporter from a Philadelphia newspaper wrote that the negotiations were taking a toll on Moffett's wife and three children. Moffett was appalled. The children are real enough, but the wife is not. He is divorced and decidedly eligible.

He is 48 but looks younger. His idea of a good time is a 10-kilometer race (personal record, set three weeks ago in Baltimore, 39 minutes 15 seconds), an imported beer and "getting a deal."

"He thrives on it," said Nancy Broff, the acting general counsel of the Federal Mediation and Conciliation Service. "Lately, he's been busy running the agency but he tends to be real happy in negotiations. Except this one is driving him nuts."

Moffett comes by his labor credentials honestly. His late father was the president of the United Mine Workers, District 50, a union with 250,000 members. Moffett got his start there. When his father had a falling-out with union higher-ups, Moffett decided to find a new job.

He arrived at the Federal Mediation and Conciliation Service as an intern in 1961 and has been the acting director since January. He came to Washington in 1967 after six years in Cleveland as a field mediator, four years at the University of Maryland (bachelor's degree in education, 1957) and two years in the Navy aboard the USS Sierra. "That's where they put all the jocks," he said. "The boxers, the ballplayers. It was like a big athletic dorm. All we did was play ball."

Moffett, who lives in Adelphi Park, got involved in baseball's labor wars for the first time in 1969. He gets the biggies: the New York newspaper strike in 1979; The Washington Post pressmen's strike in 1975; the long-shoremen; the teamsters, and the air traffic controllers, who were vying for his time, along with the baseball players.

Late Monday, after "getting a deal" to avert a strike by the controllers, Moffett said, "One for two ain't bad."

A lot of Moffett's work is done in private sessions with the parties when "you can talk straight and you're not encumbered by the other side listening.

"Almost all the work is done behind the scenes," he says, in informal sessions, and telephone calls. "What we try to do is make things happen any way we can. We try to do without people knowing it. . . Then people say, 'How did that happen?' And you say, 'Only the shadow knows.'"

He laughs at his own attempt to sound mysterious. After all, he says, "I'm just a poor boy from Pennsylvania trying to make it in the fast lane."