Ten years or so ago, as the actor Alec Baldwin remembers it, the gallery owner Mary Boone sent him an invitation to a show of work by the painter Ross Bleckner, an artist whom she represented and he had befriended.

The card featured a reproduction of Mr. Bleckner’s “Sea and Mirror,” a work from 1996, when the artist was at the height of his popularity.

So began Mr. Baldwin’s love affair with the painting — an infatuation that has ended with Mr. Baldwin, who occupies a central role in New York’s cultural life, now pitted in a bitter dispute with two formidable players in the city’s rarefied world of art and money — Ms. Boone, a prominent art dealer, and Mr. Bleckner, one of her notable talents.

This has, to say the least, become awkward.

For years, Mr. Baldwin said he carried the image of “Sea and Mirror” in his shoulder bag, alongside a picture of one of his daughters and his father. In 2010, he asked Ms. Boone to find the collector who owned it and pry it away.