Baseball held its luxuriously relaxed midsummer picnic today - the ritual reunion of celebrities at the workouts on the day before the All-Star Game.

By Tuesday night at 8:40 p.m., when Nolan Ryan starts for the American League against NL's Steve Carlton in this 50th classic, that mood will have changed. After losing 15 of the last 16 of these tilts, including the last seven in a row, the AL is, in home run leader Fred Lynn's words, "pretty sick of hearing about it."

For today, however, baseball staged one of its most pleasant pastorals. Why be blase? It was a blast - actually, one tape-measure blast after another in the tiny indoor Kingdome.

"Put the big boys in there together," crowed Chuck Tanner, a coach for the National League who was shepherding George Foster, Mike Schmidt, Dave Parker and Dave Winfield into one batting-practice foursome. "Give the folks a thrill."

Like the 10,000 open-mouthed freebies in the stands, old Lou Brock stood by the cage open-mouthed. "Is there a normal bat in here?" he asked, perusing the heavy lumber leaning against the screen. "I can't even lift these."

"See those speakers," said Danny Ozark of the NL coaching staff, pointing at a half-dozen public-address speakers hanging from the roof that can be hit by a long, high fly ball. "We may tear'em down."

The NL sluggers tried as even 40-year-old pitcher Gaylord Perry jumped in the batter's box and hit two straight pitches into the cozy left field bleachers that are only 316 feet down the line.

Signs exist, however, that NL hegemony may be waning. The American League, at last, appears to have reached parity in overall talent. In fact, it may have more and better top teams.

Nevertheless, the junior circuit knows that the final hurdle to overcoming its prestige gap is a sound victory in the All-Star Game - something that has not happened once since 1962.

"The World Series is team against team where depth and finesse are more important," said Lynn, who because of a leg injury is the only starter whose status remains in question. "The All-Star Game is power hitting and power pitching."

That's where the AL hopes it is drawing even.

"Anybody added up the homers yet?" asked Baltimore's Ken Singleton, knowing that they had. The 19 ALers actually have a large power edge over the 20 NLers - 264 homers, 1,073 RBI and a .302 team average to 241 homers, 909 RBI and .293.

"Let's see," said Baltimore reliever Don Stanhouse, going over the probable progression of AL pitchers. "Nolan starts 'em off with 110-mph heat. Then Tommy John throws those sinkers up there at 67, then Jim Kern comes back at 'em at 98 miles an hour. And we got this guy named (Ron) Guidry who might be good in the ninth inning."

At long last, the AL thinks of this game as serious business, not an inevitable crushing by the NL's superior power, speed and fast ball hurling.

Just as important, this game has an overall luster that makes the final score a secondary consideration.

Baseball has reached one of those fortunate years when its aging stars are playing with graceful eminence and its best young players finally have been recognized by the public.

The stars here truly do look like future Hall of Famers. For the nostalgic, Carl Yastrzemski of Boston, who will start at first base in place of injured Rod Carew, and Brock are both closing in their 3,000th hit.

But as the old add their glamor, an entire contingent of young bucks, all making big bucks, has arrived together. Eyeballs snap to attention when Parker, Foster, Jim Rice, Winfield, Schmidt and Don Baylor step up to crush 450-footers.

The NL's No. 2 through No. 6 hitters - Parker, Steve Garvey, Schmidt Foster and Winfield - could be compared, for raw power, to the famous quintet of the first All-Star Game in 1933: Lou Gehrig, Babe Ruth, Jimmie Foxx, Al Simmons and Joe Cronin.

In fact, Ryan, who has 160 whiffs in 145 innings and had a one-hitter in his last start, may have a memorable meeting with that cast in the first three innings.

"Ryan is the perfect pitcher for this park," said Lynn. "The ball flies out of here, if you hit it. But the lights are bad in here, so the ball looks fuzzy. It's hard to make contact. Nolan pitching in the Kingdome should be almost invisible."

"We're putting on a BP (batting practice) show," said Schmidt, "But when Ryan gets on the mound, I'll settle for a couple of balls hit anywhere."

This game has more intriguing non-related angles that seem plausible. For instance, the AL starter, Ryan, refused to be on the '77 All-Star team after feeling slighted in a previous year. So last year, AL Manager Billy Martin said Ryan "won't be on my team if he's 40-0." Now Ryan graciously says, "I may have been wrong."

On the other side, Philadelphia's Carlton, starting because the AL lineup is heavily left-handed, has a Phillie batterymate in red-hot hitting Bob Boone, who is 27 for his last 52.

While most players were delighted to be here, even if many of their eyes were red from all-night flights, one player - Garry Templeton of St. Louis, 22 - made himself an All-Star joke by announcing that he wouldn't play if he wasn't voted in as a starter. Joining Templeton in the cast of NL soreheads at shortstop was Cincinnati's Dave Concepcion, who, miffed that Larry Bowa was picked over him, pleaded off at the last minute with a mysterious leg injury. That injury, however, did not stop Concepcion from getting four RBI on Sunday.

"I'm psyched as heck just to be here, let alone getting to bat cleanup," said Schmidt, the major league home run leader now with 31 and also over the last six years. "As for Garry (Templeton), if you'd asked him 10 years ago when he was a kid if he'd like to be here, he'd have been tickled to death."

For years, Schmidt has played uncomplaining second fiddle to Pete Rose in the fan balloting at third base. With luck, Templeton someday may approach the value of the Gold Glove Schmidt. The Phillie has remembered what Templeton forgot - this is the ultimate game of childhood dreams, baseball's picnic at the end of the rainbow.

On this beautifully clear and hot afternoon by Puget Sound, it may have seemed ironic to play baseball indoors on a carpet with balls flying past PA speakers hanging from the ceiling. Yet, even in the midst of the Kingdome's bleak prison architecture, it is impossible to keep this particular cast of stars from shining.