PARIS — More than 70 years after it was plundered by the Nazis, a missing painting by Monet that depicts the shimmering blue rapids of the Creuse River has pitted two of the wealthiest and most prominent families in France against each other.


Ginette Heilbronn Moulin, 85, the chairwoman of the Galeries Lafayette department store chain, is pursuing a claim that the Wildenstein family, an international dynasty of French art dealers, is concealing information about the stolen work. The canvas, which belonged to the Heilbronn family, vanished in 1941 after a Gestapo raid on a family bank vault.


Last summer, after Ms. Moulin filed a criminal complaint against the Wildensteins, the French authorities ordered a preliminary investigation. An anti-art-trafficking squad is sifting through World War II documents to pick up the trail of the work, “Torrent de la Creuse,” Monet’s 1889 study of the confluence of the Creuse and the Petite Creuse Rivers.


“It’s not a question of the price of the painting,” Ms. Moulin said in an interview here in her art-filled apartment. “It’s a question of a victory against the Germans and ...” Her voice trailed off.


The Wildensteins, who have been selling art for five generations, have steadfastly denied any knowledge of the painting’s whereabouts. But Daniel Wildenstein, an Impressionist scholar who died in 2001, had included it in two of his widely embraced inventories of Monet’s work. In both he listed it as being in a private collection: an anonymous owner in the first reference and an unidentified American owner in 1996.


The suspicions of Ms. Moulin and her family were aroused last year when an unrelated investigation into the Wildenstein Institute, a nonprofit research organization run by the family, turned up in its stately mansion here more than 30 artworks that had been reported missing or stolen. Most were items that had vanished years earlier during the settlement of family estates. But members of one Jewish family told the police that they believed a recovered sculpture of theirs could have been looted by the Nazis because it appeared on no postwar estate lists.


Guy Wildenstein, the billionaire who leads the family business from New York, declined through his lawyers to comment on Ms. Moulin’s accusations. But he has contended that the institute never hid missing works, saying it simply lacked a full inventory of what was in its vault.


Lawyers for Mr. Wildenstein, who is Jewish, have strenuously denied that any of the seized items were Nazi loot.


The Monet vanished in a Gestapo raid on a bank vault in the southwest of France, from which 10 paintings belonging to Ms. Moulin’s father, Max Heilbronn, were taken. Heilbronn was a member of the Resistance whose French Jewish family was forced out of the historic Galeries Lafayette store on Boulevard Haussmann in Paris and replaced by Nazi collaborators. He was imprisoned in Buchenwald with other French resisters, including Étienne Moulin, who later married Mr. Heilbronn’s daughter, Ginette, and took charge of the Galeries Lafayette.


The family has recovered four of the works taken, including a Renoir painting of pastel roses that the family spotted when it came up for sale at Christie’s in 2004. Two Pissarro landscapes from the bank vault were also recovered from the Berlin home of Hermann Goering, Hitler’s second in command.


Even now, though, more than half of the artworks taken from Jewish families in France and Belgium during World War II remain missing.


What drives Ms. Moulin to keep searching after so many years?


“This painting represents some of the history of our family,” she said. “It was my grandson who pushed me to react. He doesn’t understand how this could happen.”


Ms. Moulin said that in the 1950s, her mother, Paulette Heilbronn, met with an art dealer who had a photograph of the painting, and that he pledged to recover it. But when Ms. Heilbronn approached the dealer again, he told her it was in the possession of people who were “untouchable,” Ms. Moulin said


Years later the family discovered references to the missing painting in the 1979 and the 1996 editions of Daniel Wildenstein’s five-volume inventory, or catalogue raisonné, of Monet’s work. Such catalogs list all known authenticated works by an artist and serve as something of an imprimatur. No major auction house, for example, will sell a work as a Monet unless it is listed in the Wildenstein inventory.