NEW YORK — The Museum of Modern Art has appointed Peter Galassi director of its department of photography, a move that has ended months of speculation over who would succeed John Szarkowski in one of the most highly prized curatorial positions in the field.Mr. Galassi has been a curator in the department since 1986. He organized the current photography exhibition, "Pleasures and Terrors of Domestic Comfort." The show signals a widening acceptance of photography that is not strictly modernist and at the same time reaffirms the institution's long-standing commitment to modernism and documentary approaches to the medium. Galassi becomes the fourth director of the department, founded in 1940 by Beaumont Newhall. The photographer Edward Steichen was its director from 1947 until 1962. Mr. Szarkowski followed Steichen in the position, which he held until retiring in July. Szarkowski, a highly influential presence in the field over the last three decades, was named the department's director emeritus, simultaneous to Galassi's appointment Oct. 11. Galassi was born in 1951 in Washington. He holds a bachelor's degree from Harvard College and a PhD from Columbia University. His doctoral dissertation provided the basis for his book "Corot in Italy: Open-Air Painting and the Classical-Landscape Tradition," published in May by Yale University Press. Galassi has organized 10 photography exhibitions at the museum since joining the department in 1981 as an associate curator, among them "Henri Cartier-Bresson: The Early Work," in 1987, and "Nicholas Nixon: Pictures of People," in 1988.