Shadow of a Doubt Note: The painting depicts Christ revealing himself to the Apostle Thomas and is called "the Incredulity of Thomas." The claim that it might be a Rembrandt has stretched the credulity of art experts, some of whom think it is a fake. A similar painting with the same title is in the Pushkin Museum in Moscow and some scholars believe it is the real Rembrandt . . . William Manhart of Chicago thinks differently. He quit his job as an animal keeper to prove the painting's authenticity. Manhart has dated the wood panel and paint used to 1634. The painting, which goes on display at the World's Fair tomorrow, would be worth $20 million if authentic . . . It is owned by the heirs of Florian Bojanski, who bought it in 1976 at a garage sale in Chicago. . . .

Sales Pinch Note: At the mid-point of the French Riviera's annual paean to art and self-promotion, the film "Inchon" is unofficial champ in the latter category. The film tells the story of the U.S. invasion during the Korean War with Sir Laurence Olivier as Gen. Douglas MacArthur. The film, financed by the Rev. Sun Myung Moon's Unification Church, was completed two years ago but has yet to find a distributor . . . The publicity firm of Rogers and Cowan has launched a $250,000 campaign in hopes of finding a distributor for the film, including a huge party and "Inchon" jackets . . . The film was screened last Sunday but no buyer has emerged yet. . . .

What else are they doing in France Note: Robert Bresson will be directing again after a hiatus of 3 1/2 years. His new film is called "L'Argent" and will be shot this summer in Paris . . . Dominique Sanda is shooting a spy film called "L'indiscretion" . . . Joseph Losey is directing a film called "La Truite" with Isabelle Huppert, the trout of the title. . . .