Restitution of lost wartime paintings is a common theme in the art world. But a slight twist on a common theme — confiscation by the Red Army, not the Nazis — is what’s making a rediscovered Marsden Hartley masterpiece the most important lot of today’s American sale at Christie’s.

Until recently, Hartley’s 1915 oil-on-canvas “Lighthouse” never left eastern Germany. It spent most of its life in the basement of a sleepy museum outside Leipzig, confiscated after World War II by Soviet soldiers from a German baron who knew Hartley during the go-go days of the Weimar Republic.

“This was a lost American masterwork of a high order,” the American paintings and sculpture department head at Christie’s, Eric Widing, said. “Seldom did Hartley ever achieve the sort of artistic triumph as he did when he was painting in Berlin.”

“Lighthouse” has an estimate of between $5 million and $7 million — and a hammer price that lands even at the low end of that estimate would nearly double the current $2.76 million auction record price for a Hartley. The painting is one of 140 works in this morning’s sale, which also includes the major western works of the Taos School from the collection of the New Mexico entrepreneur Arthur Stegall.

Today’s sale, which Christie’s expects could reach $65 million, comes at a time when interest in American artists is growing steadily beyond our boarders. International collectors are increasingly keen on exploring developments in American modernism before World War II, especially when it comes to works by Americans such as Hartley, Jacob Lawrence, and Milton Avery — all of whom are represented in this sale.

The freewheeling atmosphere of Berlin in the years leading up to World War I gave Hartley independence to delve into cubism and Parisian modernism. His social circle included Gertrude Stein and various artists steeped in the Blaue Reiter almanac of German Expressionism. Ironically, during this period of his life spent abroad, Hartley produced works that became quintessentially American, according to Mr. Widing.

The painting is based on Hartley’s idea of a collage. He used vibrant juxtapositions of color and incorporated Native American symbols such as snakes and salamanders — and even the American flag. A rightful owner who receives a restituted painting after a half-century typically braces himself for the wear and tear that comes with a colorful provenance. But “Lighthouse” is in remarkably good condition; it spent decades stored in a basement and was only recently discovered by its current owner and consignor, Baron von Veltheim, the grandson of a friend of Hartley’s.

“It was a time when American modernists were forcefully entering the world stage,” Mr. Widing said.

The Christie’s sale includes a work by one of the masters of American Impressionism, Childe Hassam. His “Spring in Central Park” has an estimate of between $2.5 million and $3.5 million.

The sale is also a rare opportunity to buy a work of Thomas Wilmer Dewing, a tonalist who was heavily influenced by Whistler. His “Lady in a Purple Dress” is expected to sell for between $2.5 million and $3.5 million. A perennial favorite of any American sale, a portrait of a mother and daughter by Mary Cassatt, has an estimate of between $3 million and $5 million.

A significant portion of the sale is from the Stegall Collection, one of the oldest and largest private collections of western American art. Mr. Widing said that the Taos School embodied in the major works of the Stegall Collection is becoming popular with collectors beyond the American west.

One work from Mr. Stegall’s collection is particularly remarkable. Nicolai Fechin’s “Friends,” an oil on canvas painting from the artist’s years in Taos, N.M., is an example of his many portraits of Native American children. It’s expected to sell for between $800,000 and $1.2 million.

Not all the western American paintings in today’s sale come from Stegall. “Indians Spear Fishing,” a sweeping landscape by Albert Bierstadt, is the result of the artist’s journeys though Wyoming in the late 1850s. Although western in theme, it’s vintage Hudson River School through and through. Christie’s assigns it an estimate of between $2.5 million and $3.5 million.

Perhaps the most spectacular of all the western landscape paintings in today’s sale is Thomas Moran’s “Green River of Wyoming.” Painted in 1878, it’s one of the artist’s earliest landscapes of that region, and is expected to fetch between $3.5 million and $5 million.