SAN DIEGO -- Federal investigators took three men into custody on Harbor Island Monday on suspicion of interstate travel for purposes of having sex with a minor, the FBI reported. Four others are in custody in Los Angeles for the same crime.

Phillip Todd Calvin, 43, of Dallas; David Cory Mayer, 49, of Chicago; and Paul Ernest Zipszer, 39, of Deland, Fla., surrendered without incident about 10 a.m., FBI Special Agent Jan Caldwell said. Investigators said Mayer is a psychologist who counsels sex offenders and Calvin is a dentist.

Agents arrested the three on a dock at Harbor Island after an undercover operation that started in November of 2003.

A San Diego FBI agent infiltrated the North American Man/Boy Love Association, attended two meetings according to investigators, and built up trust with other members. His affiliation led to a planned trip to Mexico, where the seven men believed they would find a safe haven where they could engage in sex with underage boys.

The requests were specific, including an age range of 8 to 14. The men were supposed to leave for Mexico on Saturday, but instead found themselves in a sting operation.

FBI Special Agent Daniel Dzwilewski said, "There were revelations by these members (that) they had previously engaged in sex with minors (at) various locations that they considered safe havens where they could do this activity. One individual mentioned Costa Rica and another mentioned Thailand."

Calvin, Mayer and Zipszer were booked into the Metropolitan Correctional Center in downtown San Diego pending initial appearances in U.S. District Court.

The men under arrest in Los Angeles include a special education teacher and an ordained minister charged with possessing child pornography.

The FBI said this is the biggest infiltration they have ever accomplished into the NAMBLA.

If convicted, the men face 15 years behind bars.