The only manager in baseball who appears to have a terminal case of mumps is Don Zimmer, whose heart it so big . . . well, it's so big it is bigger than the chaw of tobacco that makes him look like a man eating a basketball for breakfast.

On seeing Zimmer outside the Red Sox dugout the other day, Baltimore's resident imp, Earl Weaver, didn't day a word.He held his right thumb up. His face asked a silent question.

And response, Zimmer raised both thumbs quickly. He smiled until the chaw of tobacco came to rest behind his ear.His cheeks rose majestically and his eyes disappeared in this exercise of joy, for only winning baseball games is more fun for Don Zimmer than winning loose change at the race track.

That's what the thumbs-up pantomine was about, and Weaver, turning to leave, said, "Shoulda known, the way you're going."

The way Zimmer is going is great. Four times a player on a World Series team, Zimmer has not won a championship as a manager at any level, from Class A to the bigs. He's been trying for 10 years, and now he has the best team in baseball playing at its best. So the Red Sox may be 10 games ahead by the Fourth of July.

"They're put together a helluva club," Weaver said of the Red Sox, "and, naturally, the manager gets credit for that. You tell your general manager what you need and if he gets it, you're doing the job.

"If you'll notice, they traded a couple pitchers, Ferguson Jenkins and Rick Wise. And then they filled the hole with Mike Torrez and Dennis Eckersley. Torrez was a free agent, sure, but to get Eckersley they had to give up something - and they weren't afraid to give up that good-looking third baseman, the kid Teddy Cox."

Professional athletes today often believe the boss is worthless. "The manager doesn't have much to do with the performance of a team," said Fred Lynn, the Red Sox center fielder. "Zim's a good baseball man, but it's the players who win games."

Not by themselves.

Any team contending for a championship has both talent and discipline. The manager is responsible for using that talent wisely and seeing that order, not chaos, marks his team. Even that most chaotic of champions, the Oakland A's of the Reggle Jackson and Catfish Hunter days, came together between the white lines with a discipline created by the fertile mind of the manager, Dick Williams.

From the leadoff man to the ninth-place hitter, the Red Sox are formidable with the stick. They have four starting pitchers capable of winning 18 to 20 games with any first-division team. Defensively, they are excellent. The bench is sound and the relief pitching is good enough.

So any gerbil - as pitcher Bill Lee recently characterized Zimmer in one of his notorious verbal hallucinations - could manage the Red Sox, right? "All he has to do," said Lynn, "is put nine men on the field and handle the pitching rotation."

Horse, shall we say, feathers.

The most difficult job in all of sports is to do the expected. What Billy Martin did last season, winning under the mean pressure of his owner, to say nothing of his el-kooko brats in pinstripes - for winning that pennant, Martin should go directly to Cooperstown.

Zimmer then, is doing a fine job today. And that is nice. At 47, he has been in pro baseball 29 seasons. Twice struck in the head with pitchers in his players days, suffering injuries so terrible only a man whose heart belongs to the game would return to face a pitcher. Zimmer played 18 years. The last 11, he's been a coach manager.

"I was on good teams as a player (with the Dodgers' pennant winners of '55, '56, '59 and '63), but I've never been a winner as a manager," Zimmer said. "Billy Martin has won everywhere he's been. Me, never. I'd like to see how it feels."

Zimmer first managed in Class A, the bottom of the ladder, for the Cicinnati Reds' organization. After three in the minors, he took a coaching job with the Montreal Expos, leaving them in 1972 to manage the National League's San Diego Padres.

The realization of a dream, that was. He was a stubby guy, maybe 5-foot-9 and 190 pounds, not one of the classic athletes of his time. In 12 major league seasons, he hit .235. So he often sat on the bench, watching managers such as Charlie Dressen and Walter Alston. "I'd manage the game along with them, and see how many times I was right or wrong," he said.

The dream went bad quickly. Besides giving him a poor baseball team, the padres made life miserable for Zimmer with interference from the front-office types.

"I got fed up with it." Zimmer said. "I was listening to too many people, one telling me to do this, another telling me to do that. it was confusing. I just got bitter and quit. I said, 'If it has to be that way, I don't want to manage."

In two seasons, Zimmer's Padres lost 190 games. He landed a job as coach with the Red Sox and said that was all he wanted out of life, to be happly coaching theird base until he died. But in mid-1976, the Red Sox fired Manager Darrell Johnson, "and Dick O'Connell, the general manager, asked me if I wanted the job," Zimmer said.

With Lynn and Yastrzemski and Rice, who wouldn't want the job?

"You might not have wanted it in the middle of 1976." Zimmer said quickly. "The team was struggling, nothing was working, we had a few malcontents on the club."

A pause.

"And that's something we don't have now, he said.