A youth was shot in the back yesterday morning by a University police officer at the corner of Plympton and Mt. Auburn Streets, Harvard Police Chief Robert Tonis said last night.

Tonis refused to identify the youth but said that he was not a Harvard student. The youth, Tonis said, appeared to be stealing a motor-cycle when he was shot.

In his six years as head of the University Police, Tonis said, this is the first instance in which an officer has used a gun. Officers always carry pistols and are skilled in using them, he said.

The youth, described as a white male, 19 or 20 years old, is in good condition at Boston City Hospital, Cambridge police said. They refused to say whether the youth had been charged.

Tonis related the shooting: At 6:50 a.m., Harvard officer Robert A. Jones saw the youth, who appeared to be stealing a motorcycle from behind the Lampoon building.

When Jones moved to arrest him, the youth drove the motorcycle straight at the officer. Jones drew his gun and shot the youth in the back after the motorcycle had passed.

Cambridge Police Captain Alfred E. Marckini said the man continued driving after he had been shot and later appeared at Boston City Hospital for treatment. The youth said that he had been injured in a fracas earlier in the day.

The bullet lodged in the lower abdomen just above the buttocks, Marckini said, but no vital organs were ruptured.

Jones, the officer involved in the shooting incident, could not be reached for comment.