ROME, May 25 After months of intense discussions, negotiations between a New York antiquities collector and the Italian government have bogged down over a demand that she never be pursued by Italy again, several people close to the talks say. Italy is seeking the return of nine artifacts from the collector, Shelby White, contending that they were looted from its soil. Lawyers for both sides had been optimistic earlier this year that a deal could be struck. But an impasse developed over Ms. White's insistence that in exchange for the objects, the Italian Culture Ministry grant her immunity from legal action of any kind and promise not to go after anything else she owns or acquires in the future, people familiar with the talks said. Italian officials do not suggest that Ms. White or her husband, the financier Leon Levy, who died in 2003, knowingly bought artifacts whose provenance was suspect. But they say that forgoing potential investigations of any suspected wrongdoing in the future would essentially allow tomb robbers and dishonest dealers to traffic with impunity. Restricting an inquiry would be tantamount to "collaborating with the pillaging," an Italian official who is following the negotiations asserted in an interview. He said he did not want his name used because both sides had agreed not to discuss the negotiations until a formal agreement had been struck. Ms. White's spokesman, Fraser Seitel, declined to discuss the specifics of the situation, but said that Ms. White "remains hopeful that an accord will be reached." Over three decades Ms. White and Mr. Levy amassed one of the world's finest private collections of classical antiquities. Some two dozen pieces in their collection are on view in the new Greek and Roman galleries at the Metropolitan Museum of Art in New York, which were inaugurated last month. Mr. Levy and Ms. White, who is a trustee of the museum, are said to have donated about 20 million to create the galleries, whose centerpiece, a vast Roman-style court, bears their names. Some Italian negotiators had hoped that a pact could be announced in advance of the Met opening one of the biggest events of the spring art season to heighten awareness of the looting of archaeological sites. (Some critics of Italy's aggressive pursuit of foreign collections say that it has relied more on negative news media exposure than on moral suasion.) Last November the Italian Culture Ministry presented Ms. White with a list of more than 20 pieces in her collection that its investigators had tracked to dealers who Italy says have been linked to looted antiquities. (The list was narrowed to nine during the negotiations.) Those dealers include Giacomo Medici, an Italian antiquities dealer who is appealing a 2004 conviction in a Rome court for dealing in illicit archaeological artifacts, and Robin Symes, a London dealer under investigation here who has not been indicted. Italian officials say that Ms. White is under no legal obligation to return anything but that they hope to appeal to her sense of fairness. They cite recent agreements with the Met and the Museum of Fine Arts, Boston, which both transferred title of rare objects to Italy after being presented with evidence that they had been looted from there in recent decades. Italy is also negotiating for the return of antiquities from the Princeton University Art Museum and the Cleveland Museum of Art. But talks have broken down with the J. Paul Getty Museum in Los Angeles. Several of the pieces Italy is demanding from the Getty originally belonged to Barbara and Lawrence Fleischman, another important collecting couple. Adding to the pressures on the Getty, a former antiquities curator at the museum and an American dealer have been on trial in Rome since 2005 on charges of conspiring to acquire looted artifacts. The outcome of that trial and Ms. White's negotiations with Italy have been avidly awaited by the tiny network of antiquities dealers in the United States and abroad. Italian officials and archaeologists say that other collectors who have purchased artifacts in recent years from the galleries and dealers that are under Italian scrutiny may have cause for worry about their investments. "If you try and resell the objects, the cultural ministry could start an injunction, and if you try to give them to a museum, it risks being asked to give it back," said David Gill, a professor of archaeology and ancient history at the University of Wales in Swansea. "You can't be remembered as a great benefactor." In a 1999 study Mr. Gill and Christopher Chippindale, another British archaeologist, wrote that 93 percent of the objects in an exhibition of Levy-White artifacts at the Met had no established provenance.