WHITE PLAINS  Marion Jones, the track and field star who pleaded guilty in October to lying to federal agents about her use of performance-enhancing drugs and her connection to a check-fraud case, was sentenced to six months in prison at the United States District Court here on Friday.

United States District Judge Kenneth M. Karas’s decision on jail time agreed with the recommendations of prosecutors and sentencing guidelines, which were well below the maximum five years that she faced. But he also ordered her to perform 400 hours of community service during each of her two years of probation.

For about 20 minutes, the judge explained his reasoning, saying that although she admitted to the crimes, he was not convinced that she had come clean about her knowledge of the drugs that she was taking.

The community service, Judge Karas said, was in lieu of added jail time because he wanted her to “educate children and school-age athletes about the importance of competing without cheating.” He suggested that she work with the United States Olympic Committee and USA Track & Field to accomplish that goal.