Christian Colberg, a 25-year-old native of Puerto Rico who was named concertmaster of the Annapolis Symphony Orchestra in May 1993, has left that post to accept a seat in the viola section of the Baltimore Symphony Orchestra.

Philip Spletzer, the ASO's principal second violinist, has been designated the orchestra's acting concertmaster for the 1994-1995 season.

Mr. Spletzer, a former member of Florida's New World Symphony under Michael Tilson Thomas, is known locally as an excellent chamber and orchestral player.

Mr. Colberg was selected over the winter by David Zinman, the BSO's music director, and a panel of BSO players from more than 300 applicants vying for the open viola chair. He has been playing with the orchestra on the Meyerhoff Symphony Hall stage since March 8. A graduate of the Peabody Conservatory, he says he enjoyed his brief association with the local orchestra.

"I liked it a lot, and already I miss it. There are some great people in the orchestra, and I felt bad to leave," he said.

Though now a member of one of the country's busiest and best orchestras, he sounds wistful as he concludes, "If it were possible, I'd have kept Annapolis."