During batting practice this evening at the Metrodome, Carl Yastrzemski, once upon a time the symbol of all Boston Red Sox prima donnas, noticed that nobody was hitting grounders to the scrub infielders. Yaz jumped to grab a bat and began swatting fungoes as though this were proper work for a 42-year-old man with 3,221 career hits.

Minutes later, Jim Rice, once the symbol of the imperious Bosox star who barely knows bench-warmers' names, noticed a bunch of irregulars around the cage. Rice began an impromptu game of putt-putting, using a bat, ball and a batting doughnut as the golf-style cup.

Could these cheerful chaps, full of fellow feeling and modesty, be the mighty Boston Red Sox, who had won 17 of their last 20 games to be possessors of the best record in their sport?

The first month of baseball's season of rejuvenation needs no better symbol than these Red Sox. After 30 games, this franchise, which was thought moldering in disrepair just one spring ago, has the best mark in the sport--21-10.

More pertinent than that, these Red Hots of Manager Ralph Houk love to talk about a most un-Bosoxlike set of victorious virtues: pitching, defense, hitting to all fields, interest in "inside" baseball, team harmony and the ability to play as well outside Fenway Park as in it.

The Red Sox are typical of the blessed fresh air that has, presumably by pure dumb luck, wafted into the game in the first spring after the strike of '81. In all four divisions, a fine historic franchise, suddenly looking rebuilt and reborn, finds itself in first place: the Red Sox, White Sox, Cardinals and Braves.

All have batteries of young, little-known new stars. None is a disproportionately wild-spending, free-agent-grabbing imitation of the Yankees.

And, refreshingly, none suffers from the stagflation--inflated salaries and stagnant morale--that seems to have infected several of the fine teams of the recent past, including, perhaps, the Yanks, Orioles, Phillies, Royals and Reds.

Of all the emerging contenders, none tells a more charming and unlikely tale than these Red Sox, who are in the midst of one of those illuminating bursts when a team suddenly finds its confidence and its particular style of victory.

As Houk said this evening before the Minnesota Twins beat the Sox, 10-6: "Last year, these guys had doubts about themselves. I could visualize what this team might turn into. But they had to learn that winning just wasn't as hard as they thought it was."

Six consecutive singles with two outs in the sixth inning, including Randy Bush's first major league RBI, broke a 4-4 tie tonight. Bobby Castillo (1-1) pitched 3 1/3 innings for the victory in relief of Brad Havens while Bob Ojeda (1-3) took the loss.

Perhaps the proper analogy to this Boston club is the Orioles of 1977-80, which, just when they were pronounced dead by many, became most pleasing.

Those O's lost free agents Reggie Jackson, Bobby Grich and 20-game-winner Wayne Garland in the winter of '76; consequently, they had to turn to nine rookies in '77. That new blood transformed morale and gave the new stars a chance; the Birds won 97 games that season, and were in the Series two years later.

These Red Sox lost free agents Fred Lynn and Carlton Fisk and had to trade Rick Burleson and Butch Hobson, at what they considered 70 cents on the dollar discounts, before the '81 season.

Instead of destroying the club, those losses seem now to have revitalized them. "I think we've got 18 home-grown players who came up through the minors together. That helps," said Houk.

Baseball, of course, requires much more than cheerful chatter. The blistering Bostonians may have it. The Sox led the majors in scoring in '81; now, they also have a club ERA of 2.89, built on makeshift starting pitching and the deepest quality bullpen in the game.

"The Clear-Lansford-Miller trade (for Burleson and Hobson) really set the stage for this team," said Houk.

That deal, then thought to be a Boston disaster, now looks like a Boston coup. Carney Lansford is batting champ. Rick Miller, hitting .286, is the center fielder. Burleson's replacement at shortstop--Glenn Hoffman--currently has more homers (three) and RBI (20) this season than Lynn, Fisk, Burleson and Hobson combined (one and 15).

With the name stars gone, Boston's new lineup--with Lansford, Hoffman and first baseman Dave Stapleton (career average .305)--is no longer Fenway oriented. Everybody hits the ball everywhere. "We can score some runs on the road now," said Walt Hriniak, hitting coach. "You don't win with names. The game is played between the lines."

Mark Clear, also stolen in the Angel deal, is the most overpowering of four Sox relievers who have been at the heart of the current streak. The quartet of Clear (1.61 ERA), Tom Burgmeier (1.27), Bob Stanley (3.18) and rookie junk baller Luis Aponte (0.71) have prevented 83 percent of the runners they've inherited this season from crossing the plate.

In the past eight games, these four have allowed one run in 28 innings with only three walks and 20 strikeouts.

Houk's explanation of success is elementary. "People tend to overrate the 'name' players and underrate all the others. Maybe there's not really that much difference," he said. "More often than not, the other ball club beats itself. Right now, we're not beating ourselves."

Naturally, Houk knows better than to think that 30 games make a season.

"Things change overnight. Good managing is good players," Houk said, then added out the side of his mouth, "So's bad managing."