The Italian government last night claimed partial victory in its campaign to get the return of art works it says were stolen and smuggled out of the country on behalf of America's richest art institution.

The culture ministry said that after "long and complex negotiation", a deal had been reached with the Getty museum in Los Angeles to restore 40 objects - 12 fewer than first demanded.

However, there was no agreement on what is regarded as the most important work, a third century BC Greek bronze attributed to Lysippos, sculptor to Alexander the Great. Another valued item, a fifth century BC statue of Aphrodite, believed to be from the ancient city of Morgantina on Sicily, is to remain in the US for a further three years before returning.

The deal is Italy's third such: the Metropolitan Museum in New York and the Boston Museum of Fine Arts have already agreed to return jewels of their collections in exchange for the loans of works of equivalent value.

Last month, Francesco Rutelli, the culture minister and a deputy prime minister in the centre-left government, threatened to sever all links with the Getty if an accord were not reached by August. At that stage, Getty executives were insisting they would only return 26 objects, and exclude the Morgantina Aphrodite.

Marion True, a former curator at the Getty, and Robert Hecht, an American dealer, are on trial in Rome, charged with trafficking in illegally excavated objects. Hearings are due to resume in September.

Yesterday's agreement said the two sides had agreed to put off a decision on the statue attributed to Lysippos, known in the US as the Getty bronze, until a court in the eastern coastal city of Pesaro rules on its ownership.

The sculpture, of an Olympic athlete, was found in the Adriatic when fishermen snagged it in their net in 1964; the Getty acquired it in 1977. It says the find was in international waters, and therefore not on Italian soil. Rome does not contest the point, but says the bronze was brought ashore and then exported illegally.