Pitchers have a fraternal empathy that often outweighs any other consideration. They alone know how capricious their jobs can be, how performance hangs by the twin slender threads of injury and mechanics. One twinge in a muscle, one unconscious change in form, and the skill that seemed like second nature can become difficult or impossible.

Now, even Tom Seaver understands this pitcher's nightmare. For 15 seasons, the future Hall of Famer, who's returned to the New York Mets to finish his career, knew about health and fame. Last season, he learned how one small ill can beget another and that lead on to the next, until, finally, those complaints, each minor in itself, conspire among themselves like assassins.

Gradually, they infect the psyche, confuse the muscle memory and throw the body's coordination out of kilter until, in the end, they make such a wreck of a great pitcher that he must retreat and ask, "How do you throw a baseball?"

As Seaver stood in the batter's box here in Al Lang Field this week, he looked at the mound and saw this pitching disease, this occupational equivalent of delirium tremens, in its most virulent form. Seaver saw Mark (the Bird) Fidrych in the terminal stages of career disintegration. Fidrych, the child who once could hit his catcher's shin guards with every pitch, couldn't even find the plate. Half his pitches were six feet high; his strikes were slaughtered.

By the time Seaver arrived, three runs were in, three men on and only one out. Last spring, Seaver was in Fidrych's shoes. In his first spring game, with an injured thigh and awkward delivery, Seaver allowed 10 runs in one inning; the debacle ended with a homer by fellow pitcher Rick Rhoden.

That awful omen spawned an awful season. As soon as the thigh improved, Seaver caught a mysterious flu that weakened him for months. His legs wobbly, he pulled a muscle near the buttock. That, in turn, gave him shoulder and back miseries. Trying to compensate for aches and age, Seaver became a parody of Tom Terrific. By Aug. 15, he'd given up for the year. After going 14-2 in 1981, the Seaver of '82 had a 5-13 record, 5.50 ERA, no complete games, 136 hits in 111 innings and all the other statistical earmarks of a washed-up pitcher.

Cincinnati, knowing Seaver's market value was almost nil, granted his wish that he go home to expire. "The Reds had a horrible year (101 losses) . . . and I contributed more than anybody to that," says Seaver.

The Mets got Seaver for minor leaguers Lloyd McClendon and Jason Felice, neither considered a prospect by anyone outside his family, and journeyman Charlie Puleo.

So, as Seaver watched Fidrych, he saw a fellow in the same distress he bore last season. And he had pity. Seaver turned to Boston catcher Rich Gedman and said, "Just tell him to throw it out there and I'll hit into a double play."

Seaver grounded to short for a double play to end the inning. True to baseball's hard reality, that act of mercy only saved Fidrych for another inning and another shelling. "I wish I could have gone out and told him to quit moving his shoulders horizontally," mutters Seaver, as he recounts the story. "That's why he was wild and couldn't get any power. You have to work that front shoulder downward at a 45-degree angle."

A month ago, the chances of either Seaver or Fidrych making an inspirational comeback seemed slim. Now, Fidrych, who still loves the game as much as he is loved by those in the game, seems further away than ever. Seaver, however, is raising eyebrows and hopes.

In his first two games, Seaver allowed seven runs in eight innings. "I have no idea what he had wrong with him last year. All I know's he's throwin' the ball pretty good down here," said Manager George Bamberger. "I just hope people in New York aren't expecting him to win 20-22 games. That's not fair to Tom. I hope he can win 14 . . . He is 38 years old. I don't think he'll have many complete games this year . . . All I know is, sooner or later, age gets you."

Then, Tuesday here in St. Pete, Seaver turned his first corner, allowing five hits in seven shutout innings. Against formidable Red Sox hitters like Dwight Evans, Jim Rice and Tony Armas, he was comfortably in command.

"I did some things right. I progressed. I had decent control, mixed my pitches well, popped a couple of fast balls early . . . the way I've been throwing down here, I didn't think I'd be able to throw it by anyone. Physically, I'm fine . . . I'm very pleased. It's a step for me . . . I'd be happy with 15 (victories this season). If I pitch like I did today, I might make it."

Asked by the New York Times if he threw as hard as he once did, Seaver said, "Today, I threw as hard as ever."

"Really," said the paper of record, scribbling.

"But the ball just didn't get to the plate as fast," finished Seaver.

"Did I get that hook in deep," said Seaver. "I wish I could take you bass fishing with me."

This season, it will be hitters that Seaver is trying to hook. He's added a blooper curve ball and, in general, is trying to make the transition from a power pitcher to finesse pitcher. "From the first three or four pitches, the first few hitters, you tell by their reactions what you've got going for you that day," says Seaver. "I can't trust myself warming up . . . or trust my eye. The hitters tell me what's working and what isn't."

What if a reasonable facsimile of the old Seaver heater isn't available? "You pitch, you pitch . . . I wouldn't say the game is more exciting (to me) than it used to be, but it's probably more interesting, because it's more complex."

Seaver, with a 264-156 record, says he only has one personal goal left: 300 victories. Complicating his quest is a Mets team that lost 97 games last year and may be the worst since Casey Stengel moaned, "Can't anybody here play this game?"

The new Mets have an anticharm that's the opposite that of the original Mets. Dave Kingman, the legendary sourpuss, and George Foster, who makes almost $2 million a year but can't always be bothered to run to first base, are the team's current symbols. Their blood could be mixed to make a vaccine against hustle.

Bamberger--adorable old Bambi with his tall tales--says, "We gotta be better this year, 'cause we can't be worse."

Asked why a man with a heart condition would have abandoned retirement to lead this crew, Bamberger says, "I guess the grass always looks greener on the other side. But last year it was brown."

Now, thanks to Seaver, the Mets' lawn doesn't look quite so dead.