A tenured Yale professor and former Harvard lecturer is under investigation by the United States Attorney's Office for allegedly participating in the exchange of child pornography over the Internet.

Breaking a prolonged silence on the issue, Yale officials announced Tuesday that Antonio C. Lasaga, professor of geology and geophysics, resigned his position as master of Saybrook College and has taken a leave of absence from teaching pending the completion of the investigation.

The school publicly acknowledged the federal inquiry four days after Lasaga's abrupt and then-unexplained resignation. Last Friday he and his wife moved out of the master's residence of Saybrook College, one of 12 Yale student residency halls, which are similar to Harvard's upperclass Houses.

According to several Yale students, agents from the Federal Bureau of Investigation (FBI) raided the master's residence at Saybrook and confiscated several computers Friday.

Prior to the raid, the agents obtained a federal warrant to investigate Lasaga as part of a nationwide crackdown on Internet child pornography rings.

Federal law prohibits trafficking in child pornography over the Internet. No other members of the Yale community are being investigated, according to a statement issued by the university.

The Crimson has learned that Yale officials knew about the federal investigation at least a week before Lasaga's resignation.

Catherine E. McGuinn, a sophomore in Saybrook, said students in the college were informed of the master's departure in a meeting Friday evening.

"[The administration] said Lasaga was leaving for personal reasons and we weren't allowed to ask why," she said.

McGuinn's roommate, Kyle R. Labush, confirmed that college officials told students "not to pry."

"They didn't want questions to be asked," she said.

News of the circumstances surrounding Lasaga's resignation came as a surprise to both Saybrook residents

and students who had contact with him in theclassroom.

"No one saw this coming," said Jessica M.Lichtenstein, a sophomore in "Physical andEnvironmental Geology," an introductory coursetaught in part by Lasaga.

"Professor Lasaga is extremely energetic--youcan tell he's very bright, very student-oriented,"she said. "If you ever needed help you couldapproach him and he would answer questionspersonally."

"Most people are just extremely sad, not evenshocked at the scandal, but shocked at the extentof it," Lichtenstein added.

Labush agreed, saying Lasaga enjoyed theadmiration of his students and Saybrook residentsalike.

"It was a big shock," she said. "He wasprobably one of the most popular figures in ourcollege."

Before taking a post as professor ofgeochemistry at Yale in 1984, Lasaga earned hisPh.D. in chemical physics at Harvard in 1976 andserved as a lecturer in Harvard's Department ofChemistry and Geology in 1976 and 1977.

In addition to resigning his mastership Friday,Lasaga was granted indefinite leave from hisprofessorial duties, according to Tom P. Conroy,acting director of public affairs at Yale.

Conroy said Lasaga will remain on leave for theduration of the academic year.

The university has not announced plans torevoke Lasaga's tenure, but it is not clear whenhe might return to campus.

Former Trumbull College master and UniversityChaplain Harry B. Adams has been appointed interimmaster of Saybrook.

"As best we know, Adams has taken on theappointment until the end of the year or untilLasaga comes back," said Cynthia K. Atwood, a Yalespokesperson.

In a phone interview yesterday, Adams said,"It's a difficult moment for the college,obviously, but it's my sense that students aremoving ahead and proceeding with their studies andtheir lives."

"Obviously students were surprised and hurt anddisappointed because he was a divine master, andstudents feel that loss very strongly," he added.

Sources told The Crimson that Lasaga, who hadnot been arrested at press time, was active incommunity service and worked with needy children.

According to the sources, Lasaga has beenactive in the New Haven branch of the Big BrothersBig Sisters organization, which pairsunderprivileged youths with adult mentors.

No connection has been established thus farbetween Lasaga's community service activities andthe investigation.

Sources told The Crimson that Lasaga hasretired to his home in Cheshire, Conn. He and hiswife have two grown children, both of whom live inNew York City