There are two splendid reasons to visit Manhattan's Whitney Museum this summer.

One is a just opened retrospective of Andrew Wyeth's work that concentrates solely on his landscapes - some of the most haunting representational paintings to be found in 20th century art. Covering the last 60 years of the now 80-year-old artist's extraordinary career, the 120 works evoke the only two places the artist has in a painterly sense ever inhabited: Chadds Ford, Pa., and Cushing, Maine. You will want to spend a lot of time in both.The Wyeth show closes Aug. 30. The other Whitney attraction is its newly reorganized permanent collection, indefinitely on view throughout an entire floor of new exhibition space, created on the museum's fifth floor. Among other delights, there's an entire room of Edward Hopper paintings, plus wonderful examples of Georgia O'Keeffe, Alexander Calder (including "Circus"), Joseph Stella (including "Brooklyn Bridge"), Marsden Hartley, Arthur Dove, Elsie Driggs (including "Pittsburgh") and just about all the finest artists of the first half of the soon-to-expire century. Also on view is the Whitney's newly acquired "Cocktail," by Gerald Murphy, the patron withwife Sara of Picasso, F. Scott Fitzgerald, Ernest Hemingway and myriad more cultural icons of the 1920s. The Whitney is at 945 Madison Ave. (212-570-3600).

MoMA

On view at New York's Museum of Modern Art, 11 W. 53rd St. (212-708-9400), are two very important shows. Opening today and running through Oct. 13 is "Bonnard," some 90 mesmerizing and often bizarre works - including the famous nude bathroom paintings of his wife, Marthe - by Pierre Bonnard, one of the truly great modern artists.

Opening Thursday and up through Oct. 6 is a mammoth, 300-work exhibition of the art of Aleksandr Rodchenko, perhaps the greatest of Communist Russia's post-revolutionary painters