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, 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 more than 30 artworks that had been reported missing or stolen were found in a vault at the Wildenstein Institute, a nonprofit research organization the Wildensteins run from a mansion on the Right Bank. The items, most of which had vanished years earlier during the settlement of estates, were recovered in an unrelated investigation. [...]

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.