Adelyn D. Breeskin, 90, an artistic scholar and leading authority on modern art who was senior curatorial adviser at the Smithsonian Institution's National Museum of American Art, died yesterday of kidney failure at a hospital near Lake Garda in Northern Italy, where she was traveling on vacation.

Mrs. Breeskin had been a major figure in Washington's artistic community for the past 25 years, and she was widely known as the world's leading specialist on Mary Cassatt, the American impressionist painter and printmaker.

Her career as a curator and scholar spanned almost 70 years, beginning in 1918 when she joined New York's Metropolitan Museum of Art as an assistant in the print department.

She came to Washington in the early 1960s after a 32-year career at the Baltimore Museum of Art. For her last 15 years in Baltimore, Mrs. Breeskin had been director of the museum, and she was the first woman ever to direct a major American art museum.

Here she helped found the Washington Gallery of Modern Art, and she served as its director for two years, in the process helping to sensitize the nation's capital to an appreciation of avant-garde artistic works. She joined the Smithsonian after two years at the Washington Gallery.

Not until last December, at the age of 89, did Mrs. Breeskin cut her workweek back to four days at the National Museum, and until early this year she drove regularly to her office, at 8th and G streets NW, from her home in Georgetown. At the time of her death she was working on a new edition of her 1970 landmark catalogue of Cassatt's paintings and drawings.

Last December, the Smithsonian awarded her the Secretary's Gold Medal for Exceptional Service, saying Mrs. Breeskin's "inspired publications on Mary Cassatt have made her one of the best known and most loved of American artists." The museum also said her "rediscovery of the paintings of Romaine Brooks and William H. Johnson has greatly enriched the nation's collection, the history of American art and the heritage of women and minorities . . . . "

This spring the Washington Art Dealers Association gave her its first "Award for Cultural Achievement," citing her for promoting "the public's awareness and understanding of modern American art."

Mrs. Breeskin was born in Baltimore. She attended Bryn Mawr College but left before graduation for Boston, where she enrolled in an art school and took courses at Radcliffe College, and at Harvard and Boston universities.

She married a musician, Elias Breeskin, in 1920, but they were divorced 10 years later. Mrs. Breeskin returned to Baltimore with her three daughters to take the job at the Baltimore Museum. It was there, in 1936, that she gave Cassatt's graphics their first museum show.

Acting director of the museum for five years before being named director in 1947, Mrs. Breeskin is generally credited with having enlarged and enriched the museum with important acquisitions, including the Cone collection of early modernist masterworks.

She left the Washington Gallery of Modern Art for the Smithsonian in a dispute with the trustees over exhibit policies, and from 1968 to 1974 was the National Museum of American Art's curator of contemporary painting and sculpture. Among the exhibits she organized were ones on Cassatt, Brooks, Johnson, Milton Avery, H. Lyman Sayen and Bob Thompson. She was author of three books on Cassatt.

At Mrs. Breeskin's 90th birthday party just last week, two artistic works, "Dabrowsky V" by Jacob Kainen and "Black and White Tipped Flower" by James Surls were presented to the museum in her honor.

"She continually provided inspiration to artists, collectors and, most especially, her professional colleagues at the Smithsonian and in Baltimore," museum director Charles C. Eldredge said yesterday. "Her insights and energies on behalf of appreciation of art were remarkable."

Survivors include three daughters, Dorothy B. Brown of Washington, Jean Timbrell of Tenafly, N.J., and Gloria Peck of Seattle; five sisters, eight grandchildren, and four great-grandchildren.