ROME, Feb. 21 — Announcing a "new page of cooperation," the Metropolitan Museum of Art and the Italian government signed a watershed accord on Tuesday under which the Met will return 21 artifacts that Italy says were looted from archaeological sites within its borders.

In exchange for yielding the works to Italy — including a prized sixth-century B.C. Greek vase known as the Euphronios krater and a set of Hellenistic silver — the Met will receive long-term loans of prestigious objects from Italian collections.

At a joint news conference at the Italian Culture Ministry, the Met's director, Philippe de Montebello, said the agreement "corrects the improprieties and errors committed in the past."

It will "pave the road to new legal and ethical norms for the future," he added. At the same time, Mr. de Montebello said, the accord "opens a new phase of collaboration which does not deprive the millions of visitors to our museum of the opportunity to see archaeological material."

The pact, the first of its kind between Italy and a foreign museum, is being hailed as a model for settling antiquities disputes involving other Western arts institutions. In exchange for the artifacts, Italy has agreed to lend the Met "objects of equivalent beauty and artistic or historical significance."

"Italy has won, the Met hasn't lost, and what has benefited is culture," Italy's culture minister, Rocco Buttiglione, said at the signing ceremony.

Under the terms of the accord, the Met will immediately return four archaeological pieces to Italy: a red-figured Apulian Dinos (340 to 320 B.C.) attributed to the so-called Darius Painter; a red-figured psykter (circa 520 B.C.) decorated with horsemen; a red-figured Attic amphora by the Berlin Painter (circa 490 B.C.); and a sixth-century Laconian kylix, or drinking cup.

In exchange for the kylix, unique in the Met's collection, Italy has promised to lend a "first-quality" Laconian artifact to the Met for a renewable four-year period.

The four works to be returned immediately were all cited as evidence in the Italian prosecution of Giacomo Medici, a dealer who was found guilty in late 2004 of trafficking in looted antiquities. He is appealing his conviction.

Court documents relating to that conviction also cite Mr. Medici as a party in the sale of the Euphronios krater, which the Met bought in 1972 for a reported $1 million from the American dealer Robert Hecht. He is currently on trial in Rome on the same charges that could send Mr. Medici to prison if they are upheld on appeal.

The krater will be returned to Italy by Jan. 15, 2008, in exchange for a mutually agreed-upon artifact of equal importance. This month, the Met gave the Italian ministry a list of pieces that Italy might lend in exchange. All are cited in the agreement, including an Attic red-figured vase signed by Charinos, in the National Archeological Museum of Tarquinia, and a fourth-century B.C. red-figured krater from Paestum, in the Archaeological Museum in Naples. But Mr. de Montebello said these were merely "suggestions."

The Met will also transfer title to a set of 16 silver pieces dating from the third century B.C. that experts claim were illegally excavated from Morgantina, an ancient site in central Sicily. The pieces will remain on loan to the museum until Jan. 15, 2010, when they are to be replaced by loans of treasures of equal-value for a four-year period. The silver will be traded back and forth on a continuous rotating basis.

"It's a victory, even if it's taken so long to legitimize our claims over the objects," said Silvio Raffiotta, an Italian prosecutor who unsuccessfully sought the restitution of the silver during the 1990's.

Italy is now pressing the J. Paul Getty Museum in Los Angeles for the restitution of a statue of Aphrodite that experts suspect was also dug up in Morgantina. The Getty's former curator of antiquities, Marion True, is on trial here with Mr. Hecht on charges of illicit antiquities trafficking.

Despite his lack of success in the past, Mr. Raffiotta said he was not surprised that the silver pieces were finally coming home.

"Sooner or later it was bound to happen," he said during a telephone interview from his home in Sicily. "The fact is that it was embarrassing for the museum to keep them. I'm surprised that they resisted for so long."

The agreement also allows the Met to conduct authorized excavations at its own expense in Italy, the fruits of which would be lent to the Met "for the time necessary for their study and restoration."

Mr. de Montebello said that because the museum's antiquities department was busy preparing for a major reorganization of its Greek and Roman collections, it had not decided which digs it would participate in.

Although the pact applies only to 21 objects that were the subject of Italian claims, a clause in it says that "future controversies concerning archaeological assets will be resolved with the same spirit of loyal collaboration that inspired the present agreement."

In cases where "mutually satisfactory resolutions" cannot be reached, it adds, disputes will be "settled in private by arbitration."

In recent interviews, Mr. de Montebello has conceded that, on occasion, in the past the museum had received artifacts that may have been obtained in an "improper" way.

"We're no longer in an era where you ask no questions," he said at the news conference on Tuesday. "Now we look before we buy; the world has changed."

At the Villa Giulia National Etruscan Museum, a crucial repository of ancient artifacts in Rome, a tour guide led a class of elementary school children on Tuesday past a display case in the room dedicated to Cerveteri, site of an ancient city and a complex of Etruscan tombs from which the Euphronios krater is believed to have been looted.

Francesca Boitani, the museum's director, said that gallery could well be the krater's resting place when it returns from the United States.

The restitution of the krater "represents the healing of a wound," Mrs. Boitani said.

"This is another step forward," she said of the agreement. "But Italy must also hold up its own end."