BALTIMORE, JUNE 15 -- The Orioles today purchased the contract of right-hander John Mitchell from their Rochester Class AAA farm club and activated outfielder Mike Devereaux from the disabled list. Veteran pitcher Jay Tibbs was designated for reassignment and pitcher Jose (J.J.) Bautista was returned to Rochester.

Mitchell, 25, was acquired from the Mets in an offseason trade for outfielder Keith Hughes. Mitchell started the season in Baltimore, pitching nine innings in three relief appearances. He was sent to Rochester on April 30 when rosters had to be trimmed.

At Rochester he was 5-0 with a 1.57 ERA in 46 innings. He will start Saturday against the Red Sox, his first major league start since taking a 3-2 loss for the Mets at St. Louis on Oct. 2, 1987.

Tibbs, 29, was 2-7 with a 5.68 ERA in 10 starts. After offseason surgery to repair a partially torn rotator cuff, it was thought he would not even be available until midseason. But he showed up at spring training and won a job.

He said before tonight's game that he was healthy all season. Off the field, however, he had to deal with the terminal illness of his father, who died three weeks ago.

Tibbs has not necessarily been belted, as his ERA and record might indicate. He was disappointed with the club's decision, which gives him 72 hours to accept assignment to Rochester or ask for his release.

"In my eyes, there is nothing to work out," he said. "How do you work out bloop hits and bad luck? They have tried to send me down the past three years and I have proven each time that I am not a AAA pitcher. . . . This is not the end of my career by no means."

Devereaux has been out since pulling his right hamstring on May 17. He is hitting .182 for the Orioles. In a six-game minor league rehabilitation assignment this week, he hit .321.Practice Helps

In Thursday night's 8-5 loss to Milwaukee, Cal Ripken Jr. had his first three-hit game since May 12 and his first multi-RBI game since May 22. Before that game, he spent 30 minutes hitting in a cage underneath the stands with Manager Frank Robinson observing.

Ripken, who was hitting .181 in his last 26 games before tonight, has at times been criticized for taking batting instruction from no one but his father, coach Cal Ripken Sr.

Before today's game, when asked if Ripken Jr. had asked for the special hitting session, Robinson said, "Nobody comes to me for anything."