CAMDEN, N.J. (AP) _ A former school administrator and an agent for child actors are among nine men from six states charged with child pornography offenses involving children across the United States, authorities say.

''There may be hundreds, maybe thousands'' of children involved, U.S. Attorney Samuel A. Alito Jr. said Thursday.

Court papers say the two-year investigation was made possible through the cooperation of Henry Feltman Jr. of Woodbury, a commercial photographer who was arrested by local police on molestation charges in June 1985.

Under a plea-bargain, Feltman agreed to cooperate with the U.S. attorney's office after learning federal pornography charges would be pending against him, court papers say.

Feltman permitted the FBI to install audio and video surveillance equipment in his home, according to an affidavit by FBI agent Robert Winteriter that was released by Alito.

Alito said the recordings represented a breakthrough in the investigation of child pornography in the United States.

''They were trading it, they were selling it,'' he said.

A federal grand jury in Camden indicted seven of the defendants this summer. Two complaints were issued in Tampa, Fla., and Philadelphia for the other two defendants. Eight of the nine defendants have been arrested, Alito said.

He said some of the pornographic material that had been seized by federal agents appeared to be homemade.

''In order to produce pornography, you have to molest a child,'' he said.

Alito and the indictment identified the defendants arrested Tuesday and Wednesday, charged with receiving or interstate transportation of child pornography, as:

-Reade B. Nimick, 60, of Haverford, Pa., a former business manager and trustee of the Germantown Academy, a private school in Fort Washington, Pa.

-Robert David Villard, 40, of Van Nuys, Calif., an agent for child actors.

-Donald C. Hallenbeck Jr., 44, of New York City, a caption writer for The New York Daily News.

-Alan Kenneth Lefcort, 42, a computer analyst from Murraysville, Pa., near Pittsburgh, also charged with two counts of interstate transportation of child pornography.

-Joseph Fela Jr., 45, a warehouse worker from South Plainfield, N.J.

-Richard Steen Williams, 56, of Gaithersburg, Md., also charged with interstate transportation of a minor male for prostitution.

-Paul Madsen, 40, also of Gaithersburg.

-Richard F. Calligan, 55, of Kissimmee, Fla., a purchasing agent for a hotel chain.

Six had been freed on bail as of today, said Assistant U.S. Attorney Joel Rosen. Williams was being held in Maryland and Villard was being held in California, both pending detention hearings, he said.

Also charged with two counts was Herbert Bow Cruickshank, 61, of Baltimore, who previously managed country clubs in Pennsylvania and Maryland. He was not arrested because he is being treated at a National Institute of Health facility for an undisclosed illness, Alito said.