The Baltimore Orioles received memorable performances from outfielders Gary Roenicke and John Lowenstein tonight and swept a doubleheader, 7-6, 11-3, from the Seattle Mariners.

In extending their winning steak to seven, the Orioles increased their season mark to 9-1 against Seattle, pushed their record to 40-18 over American League West Division foes, improved their Memorial Stadium ledger to 38-10 and took a five-game lead over the Boston Red Sox in the AL East.

The Orioles managed their fourth twin bill sweep this season with a game-saving catch by Roenicke in the opener and a six-RBI performance, which included a grand slam, by Lowenstein in the second game.

"It makes me look awful good choosing these guys to do a job," Oriole Manager Earl Weaver said. "In spring training you choose these guys to do a job. When time comes to do it, they do it."

Roenicke, although failing to make any of Baltimore's 14 first-game hits, saved the victory when he made a leaping catch of Bobby Valentine's bid for a grand slam home run with two out in th top of the eighth. Moments earlier, the Mariners had crept within one run on Bruce Bochte's three-run homer over the center field fence against starter and winner Dennis Martinez (13-7).

"It was the most important catch of my career," Roenicke said. "I've made some catches of balls that could have meant two runs, but never four.

"I didn't know Valentine had that power. It was over the fence. The ball carried very well. I didn't jump that well. The ball surprises me the way it carried."

The catch came on a 3-2 pitch after the Mariners had reloaded the bases against reliever Don Stanhouse, who was credited with his 13th save.

"I threw the fast ball down the plate to see what he could do with it," said the Orioles' ace reliever. "He had fouled off my slider the pitch before. It was a pretty good pitch.

"I guess I provided a little excitement."

The Orioles provided plenty of batting excitement in the opener as Eddie Murray extended his hitting streak to 14 games on a four-for-four performance. He was 0-for-four in the second game, however. Ken Singleton had two hits and three runs battled in and Doug DeCinces collected two hits and two RBI.

Baltimore scored twice in the first on a triple by Kiko Garcia and doubles by Singleton and DeCinces. After Seattle closed to 4-3 in the fourth, the Orioles used a Murray double and Singleton single to begin a two-run rally in the bottom half. Singleton's homer made it 7-3 in the sixth.

There was never any doubt in game two after Lowenstein collected the second grand slam of his career in the third to highlight a five-run rally. The Orioles scored three times in the fourth for a 9-0 lead.

"I just tried to hit the ball hard some place," Lowenstein said of his grand slam. "I'm sure he (Seatle pitcher Odell Jones) was surprises I got around."

The second Oriole grand slam in three games (Pat Kelly hit one Monday night) brought a standing ovation from the 19,000 fans and forced Lowenstein to take a bow.

"You try to take the stoic approach when playing," Lowenstein said, "But moments like this, the excitement gets your adrenalin going. You go with the moment."

Singles by Lowenstein in the fourth and eighth gave him his six RBI, a team high for the season. Obtained on waivers from the Texas Rangers in the offseason, Lowenstein had only 23 RBI in 67 games before tonight.

The Orioles finished with 12 hits in game two. Al Bumbry and Mark Balenger collected two apiece. Ironically, the only starter who did not hit safely was Murray.

Over the past 15 games, Murray is 25-59 for a .424 average, raising his season mark to .295. With hits in both games, Singleton's batting streak is now at 10.

Scott McGregor went eight innings in the second game to collect his fifth win in eight decisions. He was working on a two-hitter entering the ninth when the Mariners put together a triple and three singles. Rookie reliever John Flynn fihished off the Mariners.

"The big lead early gives you extra confidence," McGregor said. "Even a grand slam can't beat you. You just throw it down the middle. They're not going to hit 11 home runs.

"It seemed awful easy."

That's what the Orioles as a team were saying. CAPTION: Picture, John Lowenstein