NEW HAVEN, Conn. — Tweedy scholars hunched over ancient documents have long been a familiar presence at Yale University's Beinecke Rare Book & Manuscript Library, one of the world's largest repositories of rare books and maps.

But a shiny X-Acto knife glinting on the floor near the seat frequented by one researcher was so out of place that a guard confronted E. Forbes Smiley III, demanding to know whether the implement was his.

Smiley owned up to possessing the razor-sharp knife. "I must have dropped it," he told the guard, according to an affidavit filed in Connecticut Superior Court.

Police say they found seven maps valued at more than $900,000 in Smiley's pockets and briefcase. The 49-year-old rare-books dealer pleaded not guilty to larceny, and will face a judge here Oct. 3.

Library theft is nothing new, but the arrest in June of a respected purveyor of antiquarian books and maps has sent nervous ripples through rare-book collections across the country.

Smiley's footsteps have been retraced, and at least three major libraries have reported finding that maps disappeared at times that coincided with his visits. An FBI art-crime squad based in Philadelphia has sent warnings to officials at the British Library in London and other foreign collections where Smiley conducted research.

Officials at Yale would not comment about a pending criminal investigation. A university spokeswoman also refused to disclose whether campus libraries had increased security as a result of the Smiley case.

"Security here is good," Dorrie Baker said. "We caught him, didn't we?"

Access to university collections of rare books and manuscripts is restricted, said Macey Morales, spokeswoman for the American Library Association in Chicago.

"Normally, the folks who have access to those types of material are part of the academic community," Morales said. "I don't think anyone off the street could walk in and say, 'I want to see your rare books.' I think there would be a certain amount of credentials they would have to produce."

Antiquarian-books expert Katherine Reagan, curator of rare books and manuscripts at Cornell University's library, said librarians had established national guidelines to help minimize the risk of theft of priceless and irreplaceable materials. She said rare-book libraries used cameras and other devices, and routinely required document users to produce identification that helped track their visits.

"But it really is impossible to eliminate this kind of theft completely," Reagan said.

She said the idea of an X-Acto knife in a rare-books collection made her feel queasy.

"That is the kind of thing that strikes fear in librarians' hearts," she said. "These materials have become very valuable. The growing value makes them more attractive targets for thieves."

Reagan said such robberies "are robbing not just the institutions, but future generations who will no longer have access to these important materials."