THE SERIES was supposed to be over after game two when, in the flush of a "mighty Casey" melo-drama, the young Dodger pitcher, Bob Welch, struck out the mighty, if preposterous, Reggie Jackson to end the ninth. Instead, what happened from that point on was that the Series became a sequence of mere baseball games, and in that sequence we saw what the sport is made of. The Yankees prevailed because they hit more singles, made fewer errors, moved more men around the bases, pitched steadler and, thanks to Graig Nettles, changed the meaning of playing third base. Except for Mr. Nettles, there was nothing spectacular about their performance; but it was relentless.

Relentlessness is exactly what the Dodgers didn't have. They relented after squawking about Mr. Jackson's base-running antics in game four; and they kept on relenting into inning nine, game six, as they watched Goose Gossage - looking both detached and driven - throw the ball past them. When Steve Garvey took a third strike for the next to last out, only Dodger manager Tommy Lasorda showed a glimmer of hope, and that was half ritualistic. In their dugout the Yankees rocked back and forth, chewed, clapped and anticipated champagne.

They had come into this 75th World Series as the Pittsburgh Pirates had come into the first - their third straight pennant; a strong, balanced team hampered by injuries. The difference was that in 1903 the Pirates lost to the Boston Pilgrims, whereas the Yankees were not to be denied. They won't it playing hurt, and coming back. They won it at the bottom of the batting order. And they won it with small heroes - Bucky Dent and Brian Doyle - who proved that the game is still played in simple acts. Even the garish championship trophy presented by Commissioner Bowie Kuhn, which looked like a church designed by Dolly Parton, couldn't damage the proceedings.

One of the odd things about this Series is that neither the Yankee comeback nor the Dodger collapse ever seemed unthinkable. Professionalism isn't always a virtue, but it was for the Yankkees, who not once gave the impression that they expected to lose. Of course, that's easier said in retrospect, where theories abound. For now, let it be said simply that the Yanks played baseball as the poet, May Swenson, has cleanly understood the game: "It's about / the ball, / the bat,/ and the mitt."