Marjorie Phillips, 90, a painter and patron of the arts who founded the Phillips Collection here with her late husband, Duncan, more than 60 years ago, died yesterday of pulmonary failure at her home in Washington.

The Phillips Collection was the first museum of modern art in the United States when it opened in the fall of 1921 when Mr. and Mrs. Phillips settled in Washington upon returning from their honeymoon. Over the years it came to include the works of Bonnard, Monet, Renoir and other great artists of the world, and Mr. and Mrs. Phillips' skill in selection and artistic display made the gallery on 21st Street NW one of the treasures of Washington's art community.

Mrs. Phillips was associate director of the museum from 1925 until her husband died in 1966, then director from 1966 until 1972. She counseled and encouraged young artists and, with her husband, made a substantial impact on 20th century art.

An enthusiastic and accomplished painter, she did family portraits, still lifes and landscapes. She liked to think of herself as a realist, like Cezanne and Van Gogh, both of whom she often evoked.

Her paintings lined the walls of her mansion on an 18-acre tract on Foxhall Road NW, where she had lived since 1929, but they also were displayed in collections at the Corcoran Gallery, Yale University and the Whitney Museum.

Twenty of Mrs. Phillips' paintings, most of them less than 10 years old, were displayed in an individual show at the Franz Bader Gallery on Pennsylvania Avenue NW when she was 81 years old. Four years earlier her paintings were the subject of an individual show at the Marlborough Gallery in London.

Born in Bourbon, Ind., Marjorie Acker grew up in Ossining, N.Y. She became an artist with the blessing and encouragement of two artist uncles, but over the objections of her father, who thought artists were too bohemian. She was one of six children, and with a sister she took turns studying one year at a time at the Art Students League in New York so that one of them would always be at home to keep their mother company and help with the other children.

In 1921 she met and married Duncan Phillips. For eight years after coming to Washington they lived on the third floor over their gallery as they built up its collection. On a trip to Europe in 1923 they were lunching at the home of Paul Durand-Ruel, a noted connoisseur and art dealer, and found themselves seated directly across from Renoir's "Luncheon of the Boating Party." They ended up buying the huge painting for $125,000, and it became the cornerstone of their collection.

The Phillipses moved in 1929 to the Foxhall Road mansion designed by architect John Russell Pope, in what was then a country neighborhood of Washington. It is now one of the most highly taxed residential properties in the city.

Their interests included politics and world affairs as well as art, and in time the Foxhall Road mansion became a salon where they entertained diplomats and politicians, and a luncheon guest was just as likely to be Walter Lippmann as Henri Matisse.

Despite the demands of her work at the Phillips Collection and the work of rearing a family, Mrs. Phillips made sure there was time in her schedule for painting. Her son, Laughlin Phillips, recalled on the occasion of his mother's 90th birthday last fall that no matter what, she went into her studio each morning to paint and closed the door behind her. She taught him to mix paints at an early age, and she taught him to use a brush when he was barely old enough to hold it.

Mrs. Phillips painted when she took her children on picnics, and she painted when she traveled, which was frequently. One of her favorites was "Summer Morning," a painting of a nurse holding her son while she watches her daughter, Mary Marjorie Phillips, ride a pony.

Although not the least bit interested in baseball, Mrs. Phillips often accompanied her husband, who was an avid fan, to games, and she took her sketch pad with her. While he followed the progress of the contest she drew the fans, the players and the scene at the stadium. Two of her baseball pictures are among her best known. One, "Night Baseball," which included Joe DiMaggio, was said to be so accurate a portrayal of the ambience at a ballgame that the Baseball Hall of Fame tried to purchase it.

In addition to her son, of Washington, and her daughter, of Devon, Pa., Mrs. Phillips is survived by two grandchildren.