The director of the Metropolitan Museum of Art, Philippe de Montebello, plans to retire by the end of 2008, the museum announced yesterday. Mr. de Montebello, 71, has been director of the Met since 1977, making him the longest-serving director in the museum’s history.

With the exception of a fouryear stint as director of the Museum of Fine Arts, Houston, Mr. de Montebello has spent his entire career at the Met, having started in 1963 in the department of European paintings.

Mr. de Montebello has presided over expansion projects that have nearly doubled the museum’s size. Most recently, in April 2007, the museum opened its new 57,000-square-foot Greek and Roman galleries, followed in the fall by the 25,000-square-foot Ruth and Harold D. Uris Center for Education.

During the last decade of his tenure, the ownership of antiquities emerged as an increasingly problematic issue for American museums, as Italy and Greece pursued repatriation of objects that they argued had been illegally excavated.

In 2006, Mr. de Montebello negotiated an agreement with the Italian government to return several disputed objects, including the so-called Euphronios krater, in exchange for long-term loans of similar objects. Although Mr. de Montebello was widely praised for making the agreement, in public speeches he expressed ambivalence, arguing that encyclopedic museums like the Met allow an international public to see such objects in the context of many traditions and cultures, and that host countries do not have a comparable ability to preserve and exhibit them.

The museum named a search committee of trustees, which will be chaired by Annette de la Renta, who is a vice chairman of the board.

Mr. de Montebello’s position is considered to be the most prominent at any art museum in the world.

The list of people who have been mentioned as potential successors includes the director of the British Museum, Neil MacGregor; the head of the Louvre, Henri Loyrette; the director of the Los Angeles County Museum of Art, Michael Govan; and the Met’s curator of 19th-century, modern, and contemporary art, Gary Tinterow. The former director of the Kimbell Art Museum, Timothy Potts, and the outgoing director of the Minneapolis Institute of Arts, William Griswold, have also been mentioned, but taking the Met job would require either of them to jump ship from a brand-new position. Mr. Potts took over as director of the Fitzwilliam Museum in Cambridge, England, on January 1, and Mr. Griswold will take office as the director of the Morgan Library and Museum in March.