A 33-year-old Washington lawyer who was convicted of two charges of sexually fondling a 13-year-old boy he was appointed to represent in juvenile court was ordered yesterday by a Virginia judge to begin serving a four-year prison term.

Roger H. Moore, who is facing disbarment proceedings in the District of Columbia following his conviction last June by an Arlington jury, pleaded with Circuit Court Judge Charles S. Russell to overturn the jury's decision that he be imprisoned.

Calling the jury verdict "draconian," the slight, bespectacled lawyer dressed in a three-piece gray, pin-striped suit told the judge he is in therapy and added that "there has been no aberrational behavior on my part since the offense."

"I am very much afraid of what would happen to me if I am sent to jail," said Moore, who was found guilty of enticing the youth into his North Arlington home and of fondling him. At the time of the June 1978 incident, the youth, one of several who testified against Moore, was facing a burglary charge in the District.

Arlington prosecutor William A. Nunn urged that Moore be imprisoned, saying that he abused his standing as a lawyer in order to gain access to his victim. "I can see no reason to tamper with the jury's verdict. All Mr. Moore had to do was to stay away from children," Nunn said.

Russell, who ordered Moore to report to the Arlington Jail Sunday to begin serving his sentence, called the case "double tragic" because of Moore's "enviable reputation as a lawyer."

"There is a strong public perception that the legal community tends to look out for its own," said Russell, "and that would be an intolerable thing in this case because Mr. Moore has been found guilty of . . . using the attorney-client relationship in the worst possible way."

Adding that he had "no wish to see him brutalized" Russell said he would recommend to Virginia's director of corrections that Moore be placed in whichever state prison the attorney chooses.