Jay Tibbs, who did not want to return to Class AAA Rochester because he felt he had proved he was "not a minor league pitcher," was traded yesterday by the Baltimore Orioles to the Pittsburgh Pirates for a player to be named later.

Tibbs, 28, had been designated for assignment on June 15 when the Orioles called up John Mitchell from Rochester. In 10 starts this season, Tibbs was 2-7 with a 5.68 ERA.

The Pirates have three pitchers on the disabled list (John Smiley, Ted Power and Bob Walk) and, with Smiley due back in the rotation this week, initially have Tibbs slotted to work middle relief.

In the National League with Cincinnati in 1984-85 and Montreal in 1986-87, he joined the Orioles in 1988 and went 4-15 with a 5.39 ERA. He seemed to turn things around in 1989, earning an early season recall from Rochester, and was 5-0 with a 2.82 ERA for Baltimore before a shoulder injury.

He had rotator cuff surgery in September and was not expected to be available before midseason but reported this spring ready to pitch.

The Pirates dropped reliever Doug Bair to make room for Tibbs. They do not have to designate the player they will send to Baltimore until Nov. 1. Horn Finds the Range

Sam Horn, who hit two three-run home runs in Baltimore's season opener but couldn't come anywhere near keeping up the pace in the American League, hit two three-run homers Sunday in Rochester as the Red Wings beat Tidewater, 11-7, in the International League.

And that's not all. On Saturday, Horn had three home runs and eight RBI in a doubleheader.