DALLAS, DEC. 8 -- In a whirlwind day of trading, the Oakland Athletics and Cincinnati Reds made the biggest move of the winter meetings, combining on a deal that might have made each a favorite to win its division. And the Baltimore Orioles learned that veteran left-hander Scott McGregor might not be able to pitch in 1988 because of what apparently is a torn rotator cuff.

The Reds, desperate for pitching, traded veteran outfielder Dave Parker, 36, to Oakland for pitchers Jose Rijo, 22, and Tim Birtsas, 27.

With Parker's acquisition, the Athletics look strong in the American League West, especially after they strengthened their pitching staff by obtaining Rick Honeycutt and Storm Davis late last season. Parker adds left-handed power to a lineup that has had mostly right-handed hitters.

The Boston Red Sox also seemed to strengthen themselves. They came here hoping to find a relief pitcher, and this morning they got one of the best, acquiring right-hander Lee Smith from the Chicago Cubs. And the price for Smith seemed stunningly low -- reliever Calvin Schiraldi and starter Al Nipper.

McGregor's injury was discovered late last season, but he has declined surgery and is attempting to rehabilitate the shoulder by strengthening the other muscles around the rotator cuff.

"It's serious," Orioles Manager Cal Ripken Sr. said. "I have a lot of doubt about how much he'll be able to pitch."

The Orioles have better news about reliever Don Aase, who had shoulder surgery last June and says he'll be ready to pitch by spring training. "There's some pain, but nothing that wasn't expected," Aase said. "Anytime you have an operation like this, there are going to be adhesions that have to break loose. I'm just starting to throw and there's some of that."

Aase said his doctors have told him he should be ready to join the Orioles' regular January throwing program in Baltimore.

The Parker trade was a disappointment to the New York Yankees, who had offered several packages of players trying to acquire the two-time National League batting champion, who will be an outfielder and designated hitter in Oakland.

"I knew there was competition for him," Oakland Manager Tony La Russa said. "We're thrilled. It gives us a lot of ways to score some runs. No question, Dave is coming to an offensive team. Rijo and Birtsas are good young pitchers, but we have some depth there."

The trade appears to strengthen the Reds, too, although it probably doesn't push them past the San Francisco Giants in the NL West. Rijo, a right-hander, and Birtsas, a left-hander, are the second and third pitchers new Cincinnati General Manager Murray Cook has acquired since the season ended. The Reds traded for Kansas City's Danny Jackson after the World Series.

Without Parker, the Reds will divide their outfield playing time among Eric Davis, Kal Daniels, Tracy Jones and Paul O'Neill.

"This provides a challenge for four young outfielders who're going to have to carry the bulk of the offense now," Cook said. "It's a matter of time inevitably marching on, and we thought the time was now."

Reds Manager Pete Rose said, "We just felt we needed some more pitching, and I like the way it's shaping up. These kids are going to have to work to make our staff, and I like that."

Parker has 273 homers in 14 seasons. He had 26 homers and 97 RBI last season, but only seven homers and 34 RBI after the all-star break.

Seconds after the Red Sox had acquired Smith, Red Sox General Manager Lou Gorman said his team "was as good as anyone in baseball."

Smith, 30, has 162 saves the last five seasons and saved 36 last season -- 20 more than the entire Boston bullpen.

"This is what we were hoping for," Red Sox Manager John McNamara said. "We paid a price in trading Schiraldi. He's going to be a good one. But we got one of the best anywhere."

Schiraldi, 25, was a star of Boston's '86 championship team when he saved nine games and won four. But he slumped badly last season, saving only six and allowing 15 homers in 83 2/3 innings. Nipper, 28, never has won more than 11 games in a season.

Privately, the Cubs were saying that Smith is not in great physical condition and appears to be aging quickly; plus, his 1988 salary is $850,000 and he's eligible for free agency after that.

"Schiraldi throws as hard as Smith and is five years younger," Cubs General Manager Jim Frey said.

The Cubs hope Nipper will go into their rotation and that Schiraldi will replace Smith as their stopper.

In a move designed to make the strike zone clearer to umpires, major league baseball's rules committee has changed the definition of a strike.

The committee changed the upper limit of the strike zone from the armpits to the midpoint between the top of the shoulders and the top of the uniform pants. The upper limit had been the armpits, but umpires almost never called strikes above the bottom of the ribs. The change should bring back the high strike . . .

The NL and AL expansion committees voted to meet with each other to study and discuss their options. The best guess is that two teams could be added by the beginning of the 1990 or 1991 season.