It was a most ironic spot for Mark Manion, a former Drexel University associate professor of philosophy who once specialized in the teaching of ethics.

Yesterday, Manion entered a Philadelphia courtroom to plead guilty to possession of child pornography and criminal use of a communication facility, or computer.

Manion, 51, of Medford, N.J., was arrested Oct. 28 after Drexel officials discovered on his university computer about 100 photographs of girls between the ages of six and eight wearing thong underwear while striking sexually suggestive poses.

The university stumbled upon the images after Manion turned his computer over to a university technician to get rid of a virus.

After the university contacted authorities in September, the Philadelphia District Attorney's Office had the U.S. Secret Service conduct a forensic search of the computer.

It turned up a total of 800 images of "pre-pubertal" girls in sexual poses and six movies of children having sex with adults, said prosecutor Jim Carpenter, assistant chief of the D.A.'s Family Violence and Sexual Assault Unit.

The search also found that Manion had made hundreds of visits to child-porn sites, including one called Lolita, Carpenter told Common Pleas Judge Karen Shreeves-Jones.

Manion and his defense attorney, J.C. Michael Bannerman, of the Patrick Artur & Associates law firm, declined a Daily News request to comment.

He resigned his position in the Department of English and Philosophy about six weeks after being arrested, according to a source familiar with the case.

Niki Gianakaris, a university spokeswoman, confirmed that Manion has resigned.

When he is formally sentenced in April, his negotiated guilty plea will spare him from going to prison but will require him to undergo seven years of "intensive" sex-offender probation, prosecutor Carpenter said.

Among the probation terms are that Manion cannot have unsupervised contact with anyone under the age of 18, cannot possess pornography, must pay a $1,500 fine, must attend a sex-offender treatment program and will have his computer monitored by specially trained probation officers, Carpenter said.

"People need to recognize that there are real victims in this case. Because people download this stuff and they pay for it they create a market for people who have children engaged in sexual acts. We're talking about young children who are five, six, even babies engaged in sexual acts with adults," he said.

Manion, whose office was on Chestnut Street near 32nd on Drexel's main campus, has a Ph.D from Temple University.

He could have faced a sentence ranging from probation to 12 months in prison but was offered the plea agreement because he had no prior criminal record, he admitted what he did and the probation term will allow authorities to monitor him for a longer period of time, Carpenter said.

Manion taught several courses in the philosophy program including engineering ethics, computer ethics, business ethics, organizational ethics and philosophy of technology, according to an online Drexel biography page.