U.S. ambassador to the United Nations Andrew Young, flanked by two State Deparment security men, spent an hour and a half yesterday waiting in a Montgomery County courthouse for a shoplifter to show up forsentencing.

The reason was that the counsel for the defense included Young's daughter Andrea, 23, who graduated from Georgetown University Law School on Monday. As a participant in the University's legal clinic, she was providing representation for the defendant under supervision of a member of the bar. Young gave his daughter a ride to the courthouse in Rockville in a State Department car. "I wouldn't be here but she had no other way of getting here except by bus," he remarked. "I thought since I was paying all the tuition, I'd stay around and see what good it's doing."

More than an hour later, Young was still waiting.So was his daughter, so was the defense attorney, and so was Circuit Court Judge John J. Mitchell. The only person absent was Andrea Young's client.

In fact, the convicted shoplifter, Phillip Stone, eventually did show up at court 2 1/2 hours after the scheduled 9:30 a.m. sentencing and after Young had left. Stone told the judge that his car had broken down. The judge give him a six-month suspended sentence for shoplifting, after Andrea Young gave a five-minute plea on Stone's behalf.