It is the rookie World Series matchup of a generation. For the Dodgers in Game 3 here Friday: Fernando Valenzuela, who is 20, looks 43 and established a stuff-of-legends reputation almost instantly this season. For the Yankees: Dave Righetti, who is 22, looks 17 and only now is showing off the equally glittering reputation branded on him three years ago.

It would have been infinitely more comfortable for Righetti if George Steinbrenner's main executive puppet at the time, Al Rosen, had not boasted in early November 1978: "We have just acquired the next Ron Guidry." This was slightly more than a month after Guidry had finished a season of dreams: 25-3, earned run average of 1.74, nine shutouts, 248 strikeouts in 274 innings.

"The first thing I did," Righetti was saying in the Yankee dugout, "was try to act like Guidry and pitch like Guidry. And that was wrong. It hurt me. I had a bad two years where I couldn't cope with the pressure. I was trying too hard."

Being Righetti, he has been the Yankees' best poststrike starter, a winner twice against Milwaukee and once in the three-game sweep of Oakland in the playoffs, with a 2.05 earned run average for the season and eight victories. In his four losses, the Yankees scored a total of only six runs.

Unlike Valenzuela, Righetti has college polish (he attended San Jose City College), and he said of the Friday showdown in which he has second billing: "It's the one place every kid all over the country wants to be. I want to take in each moment."

He does not begrudge Valenzuela, volunteering: "I think he should be MVP of the National League this year for what he's done for baseball. He's filled up stadiums for the entire league. For that, he should get it. He's a special person.

"And he can pitch."

So can Righetti.

That was obvious to nearly everyone with the Texas Rangers three years ago except the owner, Brad Corbett. Or perhaps Corbett realized this lefty laser thrower was extraordinary and still included him in that multiplayer trade with the Yankees because he desperately needed $400,000 and an established star, Sparky Lyle.

Whatever, the Yankees were certain Righetti could be a major part of their future, get them to and through several Octobers, when one of their more conservative scouts saw him strike out 21 batters in a nine-inning game for a Ranger farm team and was love-struck.

When Corbett let Righetti go, his top minor-league lieutenant, Hal Keller, quit.

"Guess I made that trade look awful for the Rangers and awful good for the Yanks," Righetti said, smiling, obviously satisfied that he had cleared the toughest hurdle in sports, fulfilling the promise expected from others. He did not want to leave the Ranger organization in the first place, and had serious reservations about joining the Yankees.

"My dad (who played shortstop in the Yankee system during the Phil Rizzuto years) got pushed around," Righetti said, "so I know what can happen in a big organization. But it (the trade to the Yankees) probably is the best thing that could have happened."

He only lately has realized that.

"Three million writers hopped in my locker when I reported to spring training in '79," he said of the instant pressure. He did not talk about Steinbrenner's early impatience or that one of his supporters, Billy Martin, was fired.

"I guess the big thing between then and now," he said, "is that I grew up a bit. I didn't change lifestyles or anything, go see a shrink. I just started throwing strikes, and going after hitters.

"I have a better-than-average major-league fast ball; I can get better-than-average major-league hitters out with it."

Righetti hopes to take that confidence to the Dodger Stadium mound.

"I'm sure they'll be more relaxed, with Fernando going for 'em, saying they've come back before after being down," he said. "But down two games to none against us they're in trouble. We're not the Montreal Expos."

Righetti realized that despite being 3-0 in the first half of baseball's silly season, he could be shipped to Yankee Siberia if he reported for the second half less than totally sharp. So he threw strikes during the strike, pitched imaginary, 100-pitch games every fifth day on a nearly empty schoolyard near his home.

Many of us have done it, taken the mound on some scrubby, stone-laden diamond with nothing around but our thoughts. We've thrown tattered baseballs across torn home plates, into and through shaky backstops; we've struck out the stars of our times, usually looking, dazzled by such speed, and now and then stepped back off the mound and basked in the applause.

This, too, was Righetti's routine.

The feeling that he belongs in the majors did not come on one pitch or one game, he said, "but just kept building. I've lost only one game on the road all year. Maybe that showed I don't crack under crowd pressure, although you don't really hear that stuff on the mound."

Righetti bristles when asked about throwing as hard as he can for as long as he can and then letting Goose Gossage save the game.. A starter, he insists, ought to try to finish, although he will take victory Friday in any manner possible.

"The pressure is on him (Valenzuela)," Righetti offered. "They're looking for him, the savior, to save 'em. I don't want to sell any of the Dodgers short, but I don't want to make 'em great hitters in my mind. You can get anybody out if you throw high and in, low and away, but it doesn't usually work that way.

"I'll go at 'em with my best. If (Steve) Garvey's a fast-ball hitter, he'll see my fast ball. I got no changeup."

He paused.

"Two rookies of the year, probably," he said to a five-deep wave of reporters. "Like a little picturebook story. I'm hoping the Yankee will come out on top."