''This is something we do not recognize because the pieces were legally granted in a temporary loan," he said. ''That is the reason it will be necessary to air this in the courts and no longer simply on the level of diplomatic conversations."
Peru's Foreign Ministry was preparing the legal case and would likely present it in Connecticut state court, Lumbreras said, adding that it was not clear when the lawsuit would be filed.
Richard Burger, chairman and director of graduate studies at Yale's Council on Archaeological Studies, did not immediately return telephone messages seeking comment.
Tom Conroy, a spokesman for the university, said he was looking into Peru's assertion that the artifacts were on loan but did not immediately have an answer.
Bingham's grandson, David Bingham of Salem, Conn., said he never heard of any promise to return the artifacts and said Yale has been a good caretaker.
''Yale has taken very good care of the stuff and it probably brought more visitors to Peru than almost any other thing because the exhibits at Yale are so famous," he said.
But Bingham said there's no reason Yale and Peru shouldn't be able compromise, assuming the country can guarantee the preservation of the artifacts. He said there are enough items to create displays in both places.
''There's enough interest where you could have a permanent exhibit in Peru, on loan from Yale, but there would be somebody who would be responsible for it," he said.
''It seems to me there's certainly a place for that to happen. But it would be a disaster if a lot of stuff got shipped down there and wasn't properly cared for."
Lumbreras said former President Augusto B. Leguia gave Bingham ''permission to temporarily export the objects for scientific ends," with the agreement that the artifacts would be returned after one year, and that the timeframe was later extended by 18 months.
''Theoretically, they should have been returned after Jan. 27, 1916," Lumbreras said. ''The fact is, they weren't returned."
For decades, Peru did not pursue the matter, he said.
