The Museum of Modern Art and the Guggenheim Foundation filed a complaint in federal court Friday, asking for a declaratory judgment rejecting a German resident’s claim that two paintings by Pablo Picasso in the museums’ collections were sold by a relative of his under duress in 1935.

The two paintings, “Boy Leading a Horse,” which is at MoMA, and “Le Moulin de la Galette,” which is at the Guggenheim, were both at one time in the collection of Paul Robert Ernst von Mendelssohn-Bartholdy, a German banker and art collector of Jewish descent. When he married his second wife, who was not Jewish, in 1927, he gifted his art collection to her, the complaint claims. In 1934 or 1935, she sold the paintings, along with three other Picassos, to Justin K. Thannhauser, a leading Jewish art dealer in Berlin. Thannhauser sold “Boy Leading a Horse” to an early trustee of MoMA, William S. Paley, in 1936, and Paley gifted it to the museum in 1964. Thannhauser kept “Le Moulin de la Galette” in his collection and in 1963 bequeathed it to the Guggenheim, which fully acquired it after his death in 1976.

The defendant, Julius Schoeps, is the grandson of von Mendelssohn-Bartholdy’s sister, but is no relation to his second wife, Elsa. In March, according to the complaint, he contacted both museums, saying that he was investigating whether the paintings were sold under duress and requesting access to the provenance information. His lawyers were given access to the provenance files, and, on November 1, Mr. Schoeps demanded that the museums hand over the paintings to him.

Mr. Schoeps recently had a similar claim dismissed in both federal court and New York State Supreme Court. In November of last year, he sued the Andrew Lloyd Webber Art Foundation in the Southern District of New York, claiming title to Picasso’s “Portrait of Angel Fernandez de Soto,” which was one of the other five paintings sold by Elsa to Thannheuser. The ALWAF was preparing to sell the painting at Christie’s that week. A federal judge dismissed the claim for lack of jurisdiction, but Christie’s nonetheless withdrew the painting from its sale. At the time, the Historic Claims and Research Director at Art Loss Register, Sarah Jackson, said that the way Mr. Schoeps pursued his action — laying claim to a much-published painting on the eve of a sale — could negatively affect other restitution efforts.

Mr. Schoeps then filed suit in State Supreme Court. On November 21, 2007, the judge dismissed that complaint, saying that Mr. Schoeps had not been appointed the personal representative of von Mendelssohn-Bartholdy’s estate. The ALWAF has instituted an action in Great Britain to defend its ownership of the painting, and Mr. Schoeps has appealed the order of dismissal.

According to the two museums’ complaint, Mr. Schoeps’ claim relies on a presumption established by a 1947 Military Law, that any transfer or relinquishment of property by a persecuted person in Germany between January 30, 1933 and May 8, 1945, was an act of confiscation. The museums’ complaint asserts that the presumption of duress does not apply, because the law is no longer in effect, and adds that, even if there were such a presumption, it would be rebutted by the evidence: namely, that von Mendelssohn-Bartholdy and his wife were able to move paintings around freely within Germany and abroad through 1935, and that they frequently did business with Thannheuser, who was himself Jewish.

MoMA’s director, Glenn Lowry, said, “This is a case where our trustees felt the evidence was so clear, and [there was] a possibility of being tied up in endless and extraordinary costly legal defenses, so it made sense to seek a declaratory judgment and try to avoid an extensive amount of litigation.”

Mr. Schoeps’s attorney, John Byrne, said he had no comment.