Two 18-year-old women have now told police that they believe they were drugged and raped at a fraternity party last weekend.

A University freshman told police Tuesday night that she was raped after possibly being drugged at the Beta Theta Pi fraternity house. Another freshman told police Friday she thinks she was drugged and raped at the same party.

The party was an unregistered semiformal event with the local chapter of Delta Delta Delta, said sorority President Martha Rothbaum. Rothbaum said she did not know at the time the party was not registered with the Social Responsibility Committee.

The sorority"s national organization is looking into the matter.

"Our primary concern is to assist our members," Rothbaum said.

The second woman said she remembered dancing with a student during the party and after waking up in a room at the fraternity thought that she had had sex with him, She also said she spent most of the day after the party vomiting.

The Ann Arbor Police Department has two male suspects, one in each rape, said Detective Sgt. Richard Kinsey.

The suspect in the incident reported Friday has been described as a black male student between the ages of 18 and 20. No information was released on the suspect in the incident reported Tuesday. No charges had been filed against either man.

Beta Theta Pi President Mike Basford would not discuss details about the incidents.

"We"re cooperating with the authorities, and when the police investigation is complete we"ll release a formal statement," Basford said.

Kinsey said there is no evidence that either woman had ingested any sort of drug, although both reported passing out. Any trace of gammahydroxy butyrate or GHB, a popular date-rape drug would be undetectable after 12 hours, before either reported the incidents.

Members of Beta Theta Pi"s national organization are participating in the investigation.

"We"re cooperating with all interested parties," said Mike Kokkinen, the fraternity"s national director of risk management. "We are looking into the possibility of having representatives (from the national office) come to help with the investigation."

IFC President Mark Hustvedt declined to comment last night because of the ongoing criminal investigation but said IFC is considering sanctions against the fraternity because the party was unregistered.

Both cases are being investigated as third-degree criminal sexual conduct, a felony punishable by up to 15 years in prison.