NEW YORK (AP)  -- Private bus companies paid nearly $1 million in bribes to four New York City school system employees in exchange for favors that included tip-offs about upcoming safety inspections, federal prosecutors said.

Three supervisors and an inspector in the Department of Education's Office of Pupil Transportation were arrested Tuesday morning on extortion, conspiracy and bribery charges.

Federal prosecutors said the men routinely accepted money over several years from bus companies that held city contracts to transport students.

The payoffs ranged from few hundred dollars to thousands of dollars, according to an indictment unsealed Tuesday. Collectively, the payments were worth tens of thousands of dollars per year, prosecutors said.

Investigators said the bribes bought a variety of benefits for the bus companies, including warnings about ``unannounced'' safety inspections and changes to bus route classifications that guaranteed the companies more city money than they deserved.

In other cases, the payoffs weren't for any particular purpose, but to generally ``secure the goodwill of the defendants,'' the U.S. Attorney's office said in a statement. The indictment said the cash started changing hands in the mid 1990s and continued until last year.

The names of the bus companies that allegedly paid bribes were not disclosed in the indictment. Only the city officials said to have received the bribes have been charged.

Arrested Tuesday were Neil Cremin, 61, of Queens; George Ortiz, 63, of the Bronx; Ira Sokol, 69, of Brooklyn, and Milton Smith, 55, of Tobyhanna, Pa.

All four pleaded not guilty and were released on bond. Cremin chuckled and declined to comment as he left the courtroom Tuesday; Smith ``looks forward to addressing the charges,'' said one of his lawyers, Carrie A. Tendler. Lawyers for the two other defendants declined to discuss the case.

The men could face lengthy prison terms if convicted.

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