Arthur Rinald Miles, the 16-year-old Largo youth convicted of killing a pizza deliveryman last spring, was sentenced yesterday to life plus 20 years in prison, despite his mother's plea for leniency for "a child who's never been in trouble before."

In a Prince George's County courtroom half filled with tearful friends and relatives of both the defendant and his victim, Judge Jacob S. Levin sighed before imposing the sentence.

"I've been here for 16 years," Levin said softly, staring at the case file before him. "It doesn't get any better."

Miles, who had no previous criminal record, was one of two persons charged in the death of Domino's Pizza employee Carl A. Krogmann, 25, of Bethesda. Krogmann was shot once in the chest the night of April 7 after Miles's accused accomplice in the robbery attempt allegedly ordered a pizza by telephone to lure Krogmann to a vacant house in Largo.

Krogmann's family applauded the sentence. "We're very pleased with what the jury has found and with what Judge Levin has done," said his father, Charles. "We appreciate the way the justice system has worked."

At his Circuit Court trial last month, Miles, who was prosecuted as an adult, admitted holding the cheap handgun used in the killing, but said it went off accidentally. The jury, apparently believing him, acquitted Miles of first-degree premeditated murder. But the jurors also ruled that Krogmann had died while the victim of an attempted robbery, making Miles guilty of first-degree felony murder, regardless of how the gun fired.

"I didn't mean no harm to anybody," Miles told Levin in a brief statement, in which he asked for "a second chance."

Noting that the jury had found the shooting to be accidental, Miles's mother, Fannie Miles, asked for leniency. "In your heart, I'm sure you've gone over that," she told Levin. "But my son is not a hardened criminal."

Miles's father, Arthur W. Miles Jr., a District police officer, followed his wife to the witness stand and echoed her plea, saying his son had fallen victim to "one weak moment." Then he looked at Krogmann's friends and relatives and added, "My heart goes out to you. I'm so sorry. It's such a tragedy. I never in my life dreamed this could happen. Not in my family."

But prosecutor Jeffrey Harding noted that a court employee who interviewed Miles wrote in a pre-sentencing report submitted to the judge that Miles "does not accept his guilt" and showed little remorse, perferring to believe he was not at fault because the gun went off by accident.

"Mr. Krogmann was a very nice young man who had a very long and happy life ahead of him," Harding told the judge. "When {Miles} went over to that house with a loaded gun, he put an end to all of that. And that's the man sitting right there who's asking you for sympathy today."

Levin was required by law to impose a life term for the murder, but could have suspended part of the sentence. He chose not to do so, and imposed an added 20 years for the robbery attempt.

In Maryland, a prisoner serving a life term is eligible for an initial parole hearing after 15 years. But several more years usually pass before parole actually is granted.

The case gained wide attention after Miles and his alleged accomplice, Roland H. Jeter, 18, were arrested. District Court Judge Gerard Devlin allowed Miles to be released on $50,000 bond. Angered by the move, Krogmann's family launched a much-publicized campaign for Devlin's ouster.

Levin subsequently revoked the bond. But a Maryland appellate panel restored it, saying Levin appeared to have been swayed by public opinion.

Jeter is waiting in jail for a trial scheduled for Oct. 29.