DALLAS — Marion Jones began her six-month sentence in federal prison today, punishment for lying to investigators about using performance-enhancing drugs and her role in a check-fraud scam.

The former Olympic track star turned herself in before noon Friday at Federal Medical Center Carswell, located on the Naval Air Station, Joint Reserve Base in Fort Worth, Bureau of Prison spokeswoman Traci Billingsley said.

Under the terms of her sentencing, she had until Tuesday to surrender to prison officials.

Although the prison specializes in medical and mental health services, it also has inmates who do not require such care. Billingsley said she could not comment on whether Jones was receiving specialized care.

Jones won three gold and two bronze medals in the 2000 Sydney Olympics, becoming perhaps the most famous and marketable female athlete in the world.

After frequently denying ever having used performance-enhancing drugs, Jones admitted she had lied to federal investigators in November 2003. Jones also admitted lying about her knowledge of the involvement of Tim Montgomery, the father of her older son, in a scheme to cash millions of dollars worth of stolen or forged checks.

Jones was sentenced in January to six months of prison time and 400 hours of community service in each of the two years following her release. She was sentenced to six months on the steroids case and two months on the check fraud case, but was permitted to serve those sentences concurrently.

Federal Judge Kenneth Karas imposed the maximum sentence suggested in Jones' plea deal, ignoring her lawyers' request for a probation-only sentence. The check-fraud scheme was a major crime, and the wide use of steroids "affects the integrity of athletic competition," the judge said.