A year after putting an American museum curator on trial on charges of acquiring antiquities illegally, the Italian government has had some impressive results. Relying on court evidence and aggressive public diplomacy, it has persuaded the Metropolitan Museum of Art and the Museum of Fine Arts, Boston, to surrender some of their finest artifacts. And ancient artworks at other museums are now firmly in Italy’s sights.

Yet negotiations have stalled with the very institution that has been Italy’s biggest target: the J. Paul Getty Museum in Los Angeles, whose former curator, Marion True, is being tried in Rome. (The proceedings resume on Friday.)

Negotiations with the Getty have been “disappointing,” the Italian culture minister, Francesco Rutelli, said in an interview on Wednesday. “I don’t think they understand the gravity of the situation,” he said. “You have a major museum, and it is exhibiting dozens of stolen artifacts.”

At issue are 52 works in the Getty’s collection that Italy says were illegally excavated and spirited out of the country. People close to the negotiations, speaking on condition of anonymity out of concern that their remarks could arouse personal antagonism and jeopardize the talks, say the Getty has made it clear that it is prepared to return about two dozen objects on the list. They add that the Italian government has struck 6 more from the original list of 52 because the evidence does not point definitively to an Italian provenance.

Yet the talks have bogged down in recent weeks as a dispute has deepened over other important pieces on the list, including a rare fifth-century B.C. limestone statue of a Greek deity, possibly Aphrodite, acquired by the Getty in 1988; and a fourth-century B.C. bronze statue of a heroic youth sometimes attributed to the Greek sculptor Lysippos, acquired in 1977.

Michael Brand, director of the Getty Museum, declined to specify which objects were in dispute or to supply specific numbers. “It’s fair to say there are some objects we both agree that will go back to Italy, and some we both agree won’t,” he said in a telephone interview. “It’s all the stuff in the middle that is the problem.”

Those works pose complicated questions for the museum as it tries to resolve the dispute with Italy without lowering the bar of proof that it will demand before returning a priceless antiquity.

Many of the works on which the two sides agree can be traced to the Italian art dealer Giacomo Medici, who was convicted on smuggling conspiracy charges in 2004, and are pictured in confiscated photographs that indicate that they were clandestinely dug up in Italy.

By contrast, the Aphrodite sculpture, whose origin has been contested for many years, was never handled by Mr. Medici, and there are no photographs indicating it was excavated from an Italian site.

The Getty bought the sculpture for a reported $18 million from Robin Symes, a London dealer. According to court records, Mr. Symes had acquired it in Lugano, Switzerland, from a Sicilian named Renzo Canavesi, who provided a document stating that it had been privately owned since 1939. In 2001 Mr. Canavesi was convicted in Sicily of having illegally exported the sculpture with false papers, but the conviction was overturned two years later.

Citing accounts from Sicilian tomb robbers, the Italian police have long argued that the sculpture was dug up at Morgantina, an important ancient site in central Sicily, the same origin given in the Italian Culture Ministry’s claim. But Malcolm Bell III, an archaeologist who has directed a dig at Morgantina for many years, says there is no scholarly evidence to suggest that the statue came from there.

In 1998 an Italian stone analysis of the Aphrodite concluded that it closely resembled stone found in parts of central-western Sicily, although it did not pinpoint a precise location. Getty officials point out that they informed the Italian government of its acquisition at the time of purchase, and no Italian claim was forthcoming. They also argue that the same kind of limestone might be found in other parts of the Mediterranean.

The bronze statue, which the Getty bought from a dealer in London for around $4 million, was discovered by Italian fishermen in the Adriatic near the Italian town of Fano in 1964. Although it was passed on to the international art market through Italy, it is unclear whether Italian patrimony laws apply to it.

“It was found in international waters, which is a whole different story,” Mr. Brand said.

Still, because of their price and rarity, both the bronze and the Aphrodite have become popular symbols in Italy of the Getty’s appetite for their country’s antiquities. They are often referred to as the Venus of Morgantina and the Fano Bronze. Their return could carry far more importance than any number of Greek vases that were sold by Mr. Medici, objects that are already plentiful in Italian museums.

More than any other major American collecting museum, the Getty has adopted tough standards to minimize the possibility of buying or accepting looted antiquities.

Last month the museum approved new measures to screen out any item whose documented provenance does not stretch back at least to 1970, the year that Unesco adopted a convention prohibiting the illicit circulation of cultural property. Mr. Brand said the new rules would make it much more difficult for the museum to buy antiquities.

Despite the negative light that the Rome trial has thrown on the collecting habits of American museums, other institutions, including the Met, have resisted adopting similar acquisition standards.

The Getty has also returned several pieces to Italy, conceding that they might have a murky past.

Yet as Ms. True’s trial resumes in Rome, the full complexity of the Getty’s predicament is being thrown into relief.

Officially, the Culture Ministry’s claim to the 52 works is utterly separate from the trial, and any accord reached to return the objects would be independent of its outcome. But the Culture Ministry is also a civil party to the case against Ms. True, and there is no doubt that the trial has added to its leverage as it seeks to obtain some of the Getty’s most prized works.

A trial hearing on Oct. 18, for example, was devoted to police testimony suggesting that the Aphrodite sculpture was dug up at Morgantina. Shortly after that hearing, Mr. Rutelli, the culture minister, suggested that the Getty’s “room to maneuver is narrowing” in negotiations with Italy.

For Getty officials, the linkage involves elaborate calculations about just how returning certain objects might affect the outcome of the trial. “There are objects we might have come to some sort of understanding about in our discussion, but there is also the legal discussion,” Mr. Brand said. “What does it mean if a piece doesn’t go back? What does it mean if it does?”

But he said he remained optimistic that the differences could be worked out, and emphasized that the Getty board was committed to resolving the dispute as soon as possible.

Mr. Rutelli, on the other hand, said Wednesday that he was “more pessimistic” than he had been in the past.

“It would not be a small thing” if the talks broke down, he said. “Until now, we have negotiated out of the spotlight, but the spotlights could light up.”