NEW YORK -- A $500,000 Monet painting that vanished from a German castle during World War II belongs to the New Yorker who bought it 30 years ago, not the original owner, a federal appeals court ruled Thursday.

The decision by the 2nd U.S. Circuit Court of Appeals reversed a lower-court ruling returning the work, "Champs de Ble' a` Vetheuil," to a West German woman whose family had owned it since 1908.

The original owner, Gerda Dorothea DeWeerth, had sued in 1983 to recover the 19th-century French impressionist oil from Edith Marks Baldinger, who bought it from the New York gallery Wildenstein & Co. in 1957.

The three-judge appeals panel found that under New York law DeWeerth "failed to exercise reasonable diligence in locating the painting after its disappearance, and that her action for recovery is untimely."

Noting that many prewar records concerning the painting have been lost, the court said that "to require a good-faith purchaser who has owned a painting for 30 years to defend (against a prior claim) under these circumstances would be unjust."

DeWeerth's New York lawyer, Joseph D. Becker, said no decision had been made on whether to appeal. His 93-year-old client lives in Bad-Godesberg, a suburb of Bonn, West Germany.

"We do think the opinion reflects an unfortunate expansion of the law of New York beyond the limits permitted to federal courts to decide," Becker said.

"I think it's an important decision for people who buy art in New York state," said Les Fagen, attorney for Baldinger.

Without the ruling, people could sue to recover artworks based on claims hundreds of years old, he said, adding: "The decision says if anyone has claims to your property, they better not sit on it."

According to court papers, DeWeerth inherited the 1879 painting, now valued at more than $500,000, from her art collector father in 1922.

In 1943 she sent the painting, which depicts a wheat field, village and trees, to her sister's castle at Oberbalzheim, for safekeeping.

Near the end of the war, when Allied occupation troops left the castle, the painting was missing, although documents reporting the theft no longer exist, said court papers.

DeWeerth sought unsuccessfully, through Allied military and West German authorities, to locate the stolen painting from 1945 to 1957.

Unbeknownst to her, the work appeared on the international art market in 1956 and was sold by a Swiss dealer to Wildenstein & Co. Baldinger purchased the painting, unaware of its wartime theft, for $30,900, the court said.

DeWeerth made no attempts to recover the painting between 1957 and 1981, when her nephew learned Wildenstein had sold it, the appeals court said.