Paris Hilton pleaded guilty yesterday to cocaine possession and was fined $2,000 by a Las Vegas judge and ordered to complete 200 hours of community service. Hilton, 29, was also given a one-year, suspended sentence and warned that any new arrests in Las Vegas would result in her going to jail. Hilton could have been jailed for up to four years on the cocaine possession charge, but she reached a plea deal with prosecutors over her arrest on the Las Vegas strip on Aug. 28. “The purpose of this is that you change your conduct,” Las Vegas justice Joe Bonaventure told Hilton at a brief hearing.