The New England School of Law yesterday announced a $25,000 reward to aid continuing efforts to apprehend the murderer of Mary Joe Frug, who was killed one year ago.

Hoping to encourage potential informants to respond to the offer, Cambridge police set up a 24-hour phone line to accept information, according to Lt. Walter Boyle.

Frug, who was a professor at the England School of Law and the wife of Professor of Law Gerald E. Frug, was stabbed to death on Brattle Street on April 4, 1991.

But while Cambridge police, state police and the Middlesex district attorney's investigators have teamed up to conduct over 200 interviews in the search for Frug's murderer, they have made little headway.

"We have a lot of information and a lot of leads, but no suspects and no motives," said Jill Reilly, a spokesperson for the district attorney.

Police have investigated the possibility that former colleagues of Frug may have borne a grudge against her for her vocal advocacy of critical legal studies, which views the legal system as a means by which the establishment perpetuates the status quo.

"We interviewed people who disagreed with her politics," Sgt. William Powers, who has headed the state police's investigation, told The Boston Globe. "But people say, "Look, when I disagree with someone, I write an article saying how stupid they are and what I believe is right. I don't go out and kill them.'"

Powers said the investigation has gotten bogged down in questioning Frug's critics at the New England School of Law and Harvard Law School.

"There have been people we have wanted to interview and we had to wait a long time, because they want their lawyers present," Powers told The Globe. "The community is so legally minded that they want to clear everything with their lawyers."

Boyle said police have pursued the investigation throughout the year.

"There hasn't been a day gone by when we haven't received a call," he said.

Reilly said Frug's murder was "a pretty unique" crime, because "we don't see crimes where a person is stabbed in a safe area like that." Cambridge's historic and prestigious Brattle St. neighborhood, where Frug was fatally stabbed, is home to many Harvard professors and Gov. William F. Weld '66.

Reilly said the Frug murder is the only case she has been in Middlesex County in which the assailant's identity was not known.

Frug, who was a Bunting fellow at Radcliffe at the time, was stabbed with a seven-inch-long, military-style blade on her way from her Sparks St. home to Sage's Jr., a grocery store on Huron Ave.

In the weeks following the murder, police interviewed many of Frug's students. They formulated a general description of the possible assailant: a brown-haired white male in his 20s. The district attorney's office postered the neighborhood with descriptions of the crime and the suspect, and also sent messages to police departments around the country in search of Frug's killer.

Police said that persons with information related to the Frug investigation should call 349-3397.