SAN DIEGO -- Dozens of San Diego State University students were arrested after a sweeping drug investigation found that some fraternity members openly dealt drugs and one even sent a mass text message advertising cocaine, authorities said Tuesday.

Of the 96 people arrested, 75 were students. Eighteen of the students were arrested Tuesday when nine search warrants were executed at various locations including fraternities, said Jesse Rodriguez, San Diego County assistant district attorney.

The undercover probe, dubbed Operation Sudden Fall, was sparked by the cocaine overdose death of a student in May 2007, authorities said. As the investigation continued, another student, from Mesa College, died on Feb. 26 of a cocaine overdose at an SDSU fraternity house, the DEA said.

Among those arrested included a student who was about to receive a criminal justice degree and another who was to receive a master's degree in homeland security.

"A sad commentary is that when one of these individuals was arrested, they inquired as [to] whether or not his arrest and incarceration would have an effect on him becoming a federal law enforcement officer," said Ralph Partridge, special agent in charge of the U.S. Drug Enforcement Administration in San Diego.

Some defendants were scheduled to appear in state court to face charges on Tuesday.

During the probe, investigators discovered that in some fraternities most members were aware of "organized drug dealing occurring from the fraternity houses by its members," the DEA said in a news release.

"Undercover agents purchased cocaine from fraternity members and confirmed that a hierarchy existed for the purpose of selling drugs for money," the DEA said.

The district attorney's office said search warrants were served in San Diego and suburban La Mesa, including the Theta Chi fraternity house and several apartments.

A member of Theta Chi sent out a mass text message to his "faithful customers" stating that he and his "associates" would be unable to sell cocaine while they were in Las Vegas over one weekend, according to the DEA. The text promoted a cocaine "sale" and listed the reduced prices.

Theta Chi's San Diego chapter declined to comment.

"We're talking to our advisers," said John Phillips, a past president of the chapter.

Dale Taylor, the fraternity's national executive director, said he was "obviously shocked and saddened" by the allegations.

Theta Chi has prohibited the San Diego chapter from group activities like parties or sports and will investigate additional disciplinary measures, up to expulsion of members or the entire chapter.

Theta Chi, based in Indianapolis, has 131 chapters in the U.S. and Canada and more than 161,000 initiates. It was founded in 1856.

The San Diego chapter was founded 61 years ago and has 65 members.

"They were on the upswing," Taylor said. "They had improved their recruitment. They were trying to raise money for a new house."

University police and federal drug agents worked together in the investigation, making more than 130 undercover drug buys at locations including fraternity houses, student parking areas and dormitories, authorities said.

Shawn Collinsworth, executive director of the national office of Phi Kappa Psi, said he was told by two of the SDSU fraternity chapter's leaders that four of its members were arrested. He said the fraternity is cooperating with the investigation.

"It isn't behavior becoming of Phi Kappa Psi," Collinsworth said.

San Diego State is one of the largest schools in California's state university system with about 34,000 students. The campus has an active network of fraternities and sororities.

• Associated Press writers Elliot Spagat in San Diego and Greg Risling in Los Angeles contributed to this report.