he tired arm of Scott McGregor and the restless bats of the Minnesota Twins combined to bring the Orioles a disastrous 9-3 loss at the Metrodome tonight.

McGregor (12-12) failed to get any of five batters out in the first inning to lose for the fifth straight time and the sixth time in his last eight decisions. By the time he left, the Twins had homered off him twice for a 5-0 lead.

Reliever Mike Boddicker yielded another first-inning home run to third baseman Gary Gaetti to make it 6-0.

"You're going to have some nights when that happens," said McGregor. "What can I say? I just didn't have anything, and it didn't take their hitters very long to figure that out."

"I saw all these guys going by the door," said Twins pitcher Bobby Castillo, who sits in the cool clubhouse runway between innings to escape from the muggy dugout, "and I said, 'What? Is this really the Twins?' "

The Orioles came to the Metrodome hoping the opportunity to play the last-place Twins would allow them to make up ground on East Division-leading Milwaukee. But the Twins foiled those plans by winning the last two of three games.

"It's no good," said Orioles Manager Earl Weaver, "especially with Milwaukee winning today. We're still in it. We're not out of it by a long shot. But we have to win to stay in it."

Coupled with Milwaukee's 10-6 victory at Oakland this afternoon, the Orioles' loss dropped them to 7 1/2 games behind the leader.

Castillo threw a six-hitter, allowing the Orioles no more than one hit in any of the first eight innings, for his second straight complete game. He struck out 10 and walked three to raise his record to 7-9.

The Orioles scored all their runs against Castillo in the ninth. Eddie Murray hit a two-run homer, his 19th, and John Lowenstein followed with his 20th home run.

Bobby Mitchell led off the Minnesota first with a single up the middle and moved to second on John Castino's hit. Tom Brunansky put the Twins ahead, 3-0, with his 16th home run.

Weaver went out to talk to McGregor but, before he had re-entered the dugout, Kent Hrbek singled to right. Then Gary Ward, the Twins' home run leader, finished off McGregor with a 423-foot homer to the retractable football bleachers in right center. It was Ward's 21st home run.

"I don't want to take anything away from their hitters," said McGregor. "I have had a tired arm for my last five or six starts and it's been a long time since I've completed a game. I was leading the league in innings for a while, but most of my innings are in the first half."