In the end, the millions of dollars worth of rare Harvard books he destroyed constituted only a fraction of the clues that led police to 42-year-old former University employee Stephen L. Womack, authorities said.

Police said yesterday that, over the past four years, Womack stole from the book collection at Northeastern, tried to extort money from that university and, in one case, threatened to blow up a bank if ransom money was not left for him at Widener Library.

Earlier this year, Womack sent letters to Widener Library and Northeastern's Snell Library saying that if they did not fire their Jewish employees, he would bomb the buildings, authorities said. The chief of Northeastern's police force also said he received a letter from Womack demanding that he fire all Jewish officers.

"This individual, the threats, and the slashings--it's all bizarre in nature," said Harvard Police Lt. John F. Rooney, the head of the criminal investigations division. "But we've got our man."

Yesterday Womack, a former Harvard library employee and part-time student at Northeastern, was arraigned in Cambridge Third District Court on multiple charges of extortion, receiving stolen property and malicious destruction. The Arlington resident pleaded not guilty to all charges.

Judge Arthur T. Sherman ordered Womack, who was arrested Wednesday, held without bail at Cambridge City Jail pending a bail hearing next week.

Harvard police say Womack is the Widener slasher, who from 1990 to 1992 terrorized Harvard library and security officials with a series of carefully planned attacks against the University's book collection.

Harvard police worked in conjunction with the FBI, the state police and Northeastern University police during a four-year investigation into the slashings.

There was no clear motive for the slashings, but many of the books were on religious subjects.

Library officials in Lexington also said last night that Womack had been mutilating books for more than a decade. Wikje Feteris, a librarian at the Lexington Public Library, said Womack had taken out hundreds of books, but only returned the covers.

'Finally Over'

The case of the Widener slasher consumed thousands of hours of police time and hundreds of thousands of dollars of University money. It was perhaps the most notorious crime in recent University history.

"It would be accurate to say that this is something which has plagued the department for years," Police Chief Paul E. Johnson said in an interview yesterday. "And it's finally over."

Authorities said they had closed in on Womack in recent months after he sent a series of extortion and bomb threat letters to police officials at Northeastern University, where he is a part-time student.

Harvard police also said Womack had sent a threatening letter to Bel- mont Savings Bank in Belmont, Mass., demanding that money be left for him at Widener Library.

Between 1991 and 1992, the slasher left notes threatening violence if anyone tried to stop him from mutilating books. One note left at Harvard said he would continue cutting out the insides of books "until the voices tell me to stop."