CENTRAL ISLIP, N.Y. — The former police chief of Suffolk County pleaded guilty on Friday to federal charges stemming from accusations that he beat a suspect in custody, threatened to kill him and then coerced his fellow officers into covering up the misconduct.

The former chief, James Burke, 51, who was known for his swaggering confidence as the leader of one of the region’s largest police departments, was subdued in Federal District Court here as the charges against him were read aloud.

“I plead guilty, Your Honor,” said Mr. Burke, wearing a drab khaki prison uniform.

Since the federal inquiry into Mr. Burke’s actions began some three years ago, investigators have expanded their inquiries and are now examining the workings of the Police Department and the district attorney’s office.

Robert L. Capers, the United States attorney for the Eastern District of New York, said the investigation was continuing and would seek out those who might have been involved in wrongdoing.