MOST of the time, arts administrators are as anonymous as the works of art they safeguard are famous. But when Martin Friedman, long-time director of Minneapolis's Walker Art Center retired last November, the ramifications of his departure were discussed in the national press. Under Mr. Friedman's 29-year tutelage, the Walker emerged as an eminent center for contemporary art. A collective sigh of relief spilled through the art world when Kathy Halbreich, who has curated several outstanding exhibitions ofcontemporary art at museums around the United States, was selected as Friedman's successor. In addition to her conspicuous commitment to living artists, Ms. Halbreich also shares Friedman's sense of obligation to popularize contemporary art without pandering to its audience. The Friedman legacy is made manifest in this hefty, comprehensive volume. Though the Walker is best known internationally for its challenging exhibitions of contemporary art, it has built a significant permanent collection. Most of the 200 paintings and sculptures reproduced here were acquired during Friedman's tenure. Taken together, they supply a proximate primer of 20th-century art movements. True to the institution's educational purposes, the book's planners have prefaced it with five overview essays that are clearly comprehensible in language and structure. They trace the development of modern American and European art, from the turn of the century to the early 1980s, framing an interpretation of modern art through extensive direct citation of the volume's illustrations. Readers who have fittingly fumed at the proclivity of art history books to make reference to works not pictured in the te xt will be gladdened by this effort. Because the essentials of 20th-century art cannot be grasped intuitively, each of the opulently illustrated works is accompanied by a concise review of the object's history, formal qualities, and place within the artist's career. Happily, the essays and reviews attend to the works in the 7 1/2-acre Minneapolis Sculpture Garden directly adjacent to the center. The Sculpture Garden is an example of those all-too-rare cooperative ventures between governments and museums. In 1988, open, city-owned land between downtown and the museum was inaugurated as home to 40 sculptural works. In addition to providing the extensive viewing areas that large-scale 20th-century sculpture requires, the tree-lined plazas and walkways encourage civic esprit de corps - a pride of place crucial to urban life. Some of the Walker's most prized sculptural works are in the garden. Claes Oldenburg's and Coosje van Bruggen's huge fountain sculpture, "Spoonbridge and Cherry" (1985-1988), has become an insouciant symbol of the center. Yet "Arikidea" (1977-1982), the complicated steel pyramid by Mark di Suvero, is just as indicative of the center's focus. Suspended in the center of the sculpture is a swing, which visitors are invited to use. As the swing sways, passengers interact with the work, and, indeed, with the whole garden. The center itself houses memorable images in modern art, such as Joseph Stella's celebratory view of the Brooklyn Bridge, titled "American Landscape" (1929), and Edward Hopper's powerful portrait of psychic tension, "Office at Night" (1940). Nevertheless, the collection's newer works are its greatest strength. Vigorous visual poems concocted by Morris Louis toward the end of his career, Chuck Close's up-close-and-personal "Big Self Portrait" (1968), and the ample fluorescent panels comprising James Rosen quist's "Area Code" (1970), testify to the energetic spirit of American art. Given the richness of the Walker's assemblage of very recent work, and the institution's dedication to public instruction, it is unfortunate that none of the overview essays deals with the way that the collection reflects tendencies in the art of the mid to late 1980s. Brower Hatcher's domed sculpture, "Prophecy of the Ancients" (1988), Anselm Kiefer's brooding "Emanation" (1984-1986), and Ashley Bickerton's brew of steel, concrete, glass, rubber, plastic, soil, rice, coffee, and peanuts, provocatively t itled "Minimalism's Evil Orthodoxy Monoculture's Totalitarian Esthetic # 1 (1989)," evince art's emergent concern with moral and environmental matters. But this is merely a quibble, made more minuscule by the quality of this book. The more enduring question confronting museums like the Walker is how they will maintain, store, and exhibit teeming collections like these, while remaining fresh in their mandate to display and explain the art of our time.