Metropolitan Transportation Authority Chairman Joseph Lhota wrote in a letter to the Manhattan District Attorney this week that "allowing ever more widespread fare-beating ... unquestionably sends a loud and clear signal to those who would flout the law." Going after fare beaters was a pillar of the "Broken Windows" theory implemented in the early 1990s. It argued that ignoring smaller quality-of-life crimes only cleared the way for bigger ones to happen. Critics said the strategy became a pretense to unfairly target poor minorities. Manhattan District Attorney Cyrus R. Vance Jr. said his policy, which took effect Feb. 1, doesn't prevent officers from stopping turnstile jumpers, and that those found to have weapons or an open warrant will be arrested and prosecuted. But a review by his office found that two-thirds of all those arrested in Manhattan for the crime had no prior convictions, and a judge posed no criminal sanctions on those who pleaded guilty, Vance said.