The suspected leader of a drug trafficking ring was among seven students who pleaded not guilty Thursday to charges stemming from an undercover operation at San Diego State University that netted more than 100 arrests.

Kenneth Ciaccio, an honors student at the 34,000-student school, is accused of selling cocaine twice to government agents. He faces up to six years and four months in prison in convicted.

"Ciaccio was identified early as a main source," Deputy District Attorney Shawn Tafreshi said during the court hearing.

Ciaccio and six others pleaded not guilty to selling an array of drugs including marijuana, Ecstasy, hallucinogenic mushrooms and cocaine. All but one remained in custody in lieu on bonds ranging from $10,000 to $150,000 for Ciaccio.

Ciaccio, 19, was among 13 fraternity members arrested in morning raids Tuesday at nine locations near the university, including fraternity houses and off-campus housing. University officials said 33 students have been suspended as a result of the busts.

Ciaccio's lawyer, Michael Messina, said he had not seen any evidence proving that his client was at the center of the ring purportedly operating out of the rundown Theta Chi fraternity house, a block off Fraternity Row.

"I do not believe he's the main guy," Messina said after the court hearing.

Campus police asked undercover federal agents for help infiltrating the university's drug scene after the cocaine overdose death of a freshman sorority member in May 2007. Authorities said they ultimately targeted an array of overlapping drug networks, some operating out of fraternities.

Federal officials said 128 people, including at least 75 university students, were arrested during the five-month investigation. That figure includes students detained for minor drug offenses or other infractions turned informants for federal agents in the probe.

Tafreshi said Ciaccio bragged to undercover agents that he could procure a quarter-pound of the drug for $2,300. According to court papers, he sent a mass text message to clients advertising cut-rate specials before leaving town for the weekend.

A 21-year-old member of Delta Sigma Pi fraternity suspected of dealing drugs, including Ecstasy, from a university parking lot across the street from Fraternity Row was ordered held in lieu of $25,000 bond. According to court papers, Thomas Watanapun made no effort to conceal the cash he made from dealing, driving directly from one deal to a bank to deposit $400.

"It's a matter where, due to peer pressure and poor judgment, he finds himself in this predicament," said attorney Nathan Aguilar in court.

Another student found with two semiautomatic weapons along with $15,000 worth of marijuana and cocaine could be sentenced up to 11 years and eight months, said Deputy District Attorney Damon Mosler.

Lawyers for two students who pleaded not guilty to marijuana charges Wednesday said their clients should not have been lumped in with those involved in trafficking.

"It seems a little heavy handed to go into a college campus with DEA agents to ferret out students who are selling small amounts of marijuana," said attorney Gretchen Von Helms. Her client, 19-year-old Joshua Matsuda, faces up to 3 years and eight months in jail if convicted on charges of possessing marijuana for sale.

His roommate, Jarrod Skippon, faces similar charges after agents allegedly found marijuana and 30 vials of hash oil at their apartment. Skippon's lawyer, Marc Carlos, said a female undercover agent asked his client to sell her pot after they met at a party.

"We're talking about a 19-year-old," Carlos said. "So they're caught in the sting, and they're being asked to put agents in touch with sellers."

The students, both freshmen, have each been released on $10,000 bail.

Other colleges in the San Diego area have also been targeted by authorities investigating drug sales.

The San Diego Sheriff's Department said about a dozen San Diego gang members set up shop in a luxury apartment building next to the Cal State San Marcos campus, about 40 miles north of San Diego. Sheriff's Sgt. Gary Floyd said the group sells marijuana, methamphetamine and Ecstasy.

Deputies have made seven arrests since late February, but the sergeant says the gang is still active. The gang members are believed to be part of a southeast San Diego gang forced out of town by an injunction.