BALTIMORE, JULY 20 -- Baltimore Orioles' Manager Frank Robinson said he won't let Ben McDonald pitch nine innings Saturday night in his long-awaited first major league start.

McDonald has relieved in 12 games -- six at the end of last season and six this year. He has been impressive in 1990, giving up only one earned run and seven hits in 9 2/3 innings.

He started seven games earlier this year in Rochester, compiling a 2.86 ERA.

He said he's excited -- but not too excited -- about starting against the Chicago White Sox.

"I'm trying to stay focused," he said. "I have to make sure I'm not too pumped up. If you get too excited, you can overthrow and lose control."

"He has some major league innings under his belt now," pitching coach Al Jackson said. "We're not throwing him to the wolves. But we had to take the wraps off him sometime." . . .

Robinson was booed Thursday night when he pulled starting pitcher John Mitchell with a runner on base and two outs in the ninth inning in favor of closer Gregg Olson. The Orioles were leading, 4-1.

"No one likes to be booed," he said. "But it won't affect my decisions about this ballclub. If I had left him in and we had lost the game, I wouldn't have been able to live with myself. . . .

Mike Mussina, the Orioles' No. 1 pick in the June draft, pitched four scoreless innings for Class AA Hagerstown Thursday night, giving up two hits and no walks and struck out two. His first professional start last Saturday was rained out after two innings. . . .

Chicago Bulls basketball star Michael Jordan is to take batting practice with the White Sox Wednesday in Chicago. . . .

Coming into tonight's game, the Orioles' bullpen had a 2.67 ERA, second in the AL behind Oakland's 2.16. . . . Brian Holton was available tonight for the first time since having two impacted wisdom teeth pulled Wednesday.