Baltimore's Scott McGregor, with a slight weakness in his throwing arm and a hefty earned run average of 7.92, found strength tonight in the Coliseum by pitching a three-hit shutout to beat the Oakland A's, 3-0.

It was the first victory for McGregor (2-4) since the opening week of the season and came a week after he was diagnosed as having two weak spots in his left arm.

McGregor, who hadn't gotten out of the seventh inning all season, allowed singles in the third, sixth and seventh innings and finished strongly.

"I set 'em up by getting crushed four straight times," said McGregor. "I'm not out of the woods yet, but it sure feels good. Just to get past the fifth inning was a lift to my ego."

The only run McGregor really needed was Larry Sheets' RBI single in the fourth. But the Orioles scored two more runs in the fifth off Oakland's Don Sutton (3-5) on a run-scoring single by Lee Lacy and a sacrifice fly by Eddie Murray.

McGregor, despite his early season troubles, has seemed like his usual affable, personable self. That might be one reason the Orioles didn't worry about him as much as they might have some other pitcher.

"Scotty's a great kid; always has been," Baltimore Manager Joe Altobelli said before the game. "He's been through a few of these little funks before, and it's not the easiest thing in the world to deal with. But Scott's such a level guy. When he's pitching well, there's no popping off."

And with McGregor pitching poorly, there had been no sulking, even though he missed his last start. McGregor, who had the best winning percentage of any pitcher in major league baseball between 1979 and 1984, did not even make it past the fourth inning in four of his seven previous starts.

In this case, the numbers are all one needs to see how much trouble McGregor has been having. In 30 2/3 innings pitched before tonight, McGregor had allowed 43 hits, nine of them home runs.

An exam in Baltimore last Thursday revealed a degree of weakness in his pitching arm, which is why McGregor decided to miss his start last weekend in Seattle and work on rebuilding strength in the arm.

McGregor started extremely well tonight. He retired the first six batters on pop-ups and fly balls, and had two out in the third before Alfredo Griffin singled to right center.

The Orioles had much better success with Sutton early on. In the fourth with two out, Fred Lynn singled and went to second on a wild pitch. Sheets got just enough bat on the ball to bloop it into right field for a single, scoring the run to make it 1-0 in favor of Baltimore.

The Orioles scored two more in the fifth. Rich Dauer and Rick Dempsey singled. The looping single by Dempsey hung in the air long enough to be caught, but shortstop Griffin apparently didn't see the ball right away, possibly distracted by Dauer breaking for second on the hit and run.

Dauer scored on Lacy's line single to center, making it 2-0. And after a sacrifice bunt attempt failed and a walk to Cal Ripken, Murray hit a fly ball that scored Lacy, to give the Orioles a 3-0 lead.

McGregor, meanwhile, was having minimal trouble. He retired the A's in order in the fifth. The sixth was a little more adventuresome. Dave Collins hit a ball that forced Jim Dwyer to make a leaping catch against the left field wall. Carney Lansford reached first on a dinky little hit. But McGregor snatched Steve Henderson's line drive that was headed for center field.

In the seventh, the A's put two men on base for the first time all night. McGregor walked Dave Kingman, and Dusty Baker singled on the first pitch, to left field.

Mike Heath basically killed whatever rally Oakland had going when he grounded to Dauer. With Kingman dallying between first and second, Dauer alertly threw to Murray to retire Heath, and Murray threw back to Ripken, who tagged out Kingman.

Perhaps the toughest thing about facing Oakland's lineup, which is packed with good hitters, is that when a pitcher finally gets through the meat of the order he still has to face Mike Davis, the American League's home run and RBI leader, in the No. 7 spot.

A lot of people don't understand why Davis, who also hits for average (.341 before tonight's game), bats so low. Altobelli said he liked the idea of not putting pressure on a 25-year-old player (who his having his first good season) by jumping him up in the order.

Davis came up with a man on third. Lynn needed all 397 feet in center field to track down his fly ball, but the inning ended, just the same. Strike Power Probable Associated Press

CHICAGO, May 22 -- Both sides in the major league baseball contract talks say they expect strike authorization to be given to union negotiators Thursday when the executive board of the Major League Players Association meets in Chicago.