The dismissed director of one of Mexico's major national police forces left the country yesterday, apparently heading into voluntary exile following revelations of the force's involvement in drug trafficking.

Jose Antonio Zorrilla, former chief of the Federal Security Directorate, flew to Madrid a day after the government signaled that it would not permit him to run for Congress in elections July 7. He had left his job as head of the directorate in early March, ostensibly to become a candidate for the Chamber of Deputies. But Mexican political sources have said he was dismissed as part of the current cleanup of police agencies.

Zorrilla is the highest official to lose his job in the housecleaning. The government has dismissed police suspected of corruption but has not filed charges against them.

Zorrilla left for Madrid a day after his family had flown there, airline officials said. He declined to say anything to reporters who questioned him at the airport.

The directorate is a plainclothed detective force that functions as a domestic political police. It is a branch of the influential Interior Secretariat, and its principal responsibilities are political surveillance and internal security.

More than 400 of the directorate's 2,200 agents have lost their jobs in the purge since Zorrilla was replaced.

Zorrilla has achieved particular notoriety because his signature was on a police credential found in the possession of accused drug kingpin Rafael Caro Quintero when Caro Quintero was captured in April. He also has drawn criticism in the media for allegedly mishandling the investigation into the slaying a year ago of Mexico's most prominent investigative reporter, Manuel Buendia. A group of journalists and others has found that the reporter was looking into official involvement in drug trafficking at the time he was killed, Buendia's old newspaper, Excelsior, reported today.