CANNES, France (AP) _ Thirteen works of art worth about $17 million were stolen from the Riviera home of Pablo Picasso's granddaughter in what police called one of the biggest art thefts ever.

Police declined to reveal the titles of the works, which were stolen Sunday morning from Marina Picasso's villa in Cannes.

Ms. Picasso was on vacation in Megeve at the time of the break-in, which police said took place while a guard was out shopping.

Police estimated the value of the stolen artwork at $17 million, and said it included two paintings by Henri Matisse, a bust by Auguste Rodin and seven paintings by Picasso.

Maurice Rheims, a Picasso expert who was appointed by the government to help divide up the multibillion-dollar Picasso estate after the painter's death in 1973, knew the collection and said he thought the value estimate was low.

''I don't know what the thieves will do with the paintings,'' Rheims said. ''They all have been inventoried, catalogued and photographed many times over. No serious art dealer or collector would touch them.''

An official at the Picasso Museum in Paris said the collection was shown in 1980 in West Germany and Italy and described it as ''impressive.''

''If anyone tries to sell them, they're crazy,'' the official said, speaking on condition of anonymity. ''They would all be known.''

Ms. Picasso, who inherited the works from her grandfather, returned to Cannes on Monday but declined to speak to reporters who had gathered at the three-story villa.

Police said they believed a single thief who was familiar with the house entered it without using force. Investigators said a sophisticated burglar alarm did not function and none of the five guard dogs was disturbed.

Ms. Picasso is the daughter of Paul Picasso and his first wife, Emilienne. Paul, who was estranged from his father at the time of his death, was Picasso's only child by his first wife, the Russian-born dancer Olga Kokhlova.