The unceasing round of Washington art shows, many of them blockbusters, has tended to obscure an important point about the city's spectacular array of art museums. The permanent collections on display in the nation's capital are in themselves blockbusters that far outshadow anything to be seen in any other American city. This guide is a quick survey of what can be seen, free of charge, in season and out, across the city. NATIONAL MUSEUMS The National Gallery of Art Constitution Avenue at Sixth Street NW. 737-4215; 842-6188.

Since the opening of the National Gallery's $94.4 million I. M. Pei East Building in 1978, it has become the nation's premier showplace. But excitement over the string of extraordinary exhibitions the East Building has hosted should not eclipse the wonders within the original West Building, one of the great picture galleries of the world.

Given its late start, the gallery's collection of art from medieval times to the present is something of a miracle. By purchase or plunder, European royalty had been gobbling up masterpieces for centuries by the time the National Gallery opened in 1941. Andrew Mellon's core collection of 125 paintings could not have been made without what former National Gallery director John Walker has called "the greatest opportunity that has occurred in the 20th century," the Russian Revolution.

That "opportunity" made possible, in 1930, the purchase of priceless old master paintings from the once-royal collections of Leningrad's Hermitage. For $6.6 million, Mellon acquired 21 masterpieces, among them Botticelli's "Adoration of the Magi," Van Eyck's "Annunciation," Raphael's "Alba Madonna," Titian's "Venus with a Mirror" and three Rembrandts. He missed out on two paintings by Leonardo da Vinci, but his heirs put that right with the purchase of the portrait of "Ginevra de' Benci" in 1967 for a reported $5 million. It is the only painting by Leonardo in America, and a crown jewel of the collection.

Today the National Gallery boasts 2,500 western European and American paintings, all acquired by gift from no less than 1,000 individuals. The gallery is currently sustained by $30 million per year from the federal government, but not a single work of art has ever been purchased with government funds. The National Museum of American Art Eighth and G Streets NW. 357-1300.

After a century and a half as a stepchild within the Smithsonian family, the National Museum of American Art began to take on its own identity in 1968 when it moved into the historic Patent Office Building, which it shares with the National Portrait Gallery. It is the only federally supported museum devoted exclusively to recording, researching and exhibiting the history of American painting, sculpture and graphics.

Starting as an odd-lot of collections given to the U.S. government by various donors, the NMAA has almost doubled its collection since 1968, and now owns 27,000 18th, 19th and 20th century American works. Among the masterpieces are "Jonah" by Albert Pinkham Ryder (one of 18 of his paintings in the collection), "The Sierra Nevada in California" by Albert Bierstadt and Morris Louis' "Delta Upsilon."

In 1972, the museum opened the Renwick Gallery, 17th Street and Pennsylvania Avenue NW, devoted to the display of crafts, decorative arts and design, and named after the architect who built it to serve as the original Corcoran Gallery of Art. The 1902 Barney Studio House, the showplace-salon-residence of artist Alice Pike Barney (1857-1931), is also administered by NMAA. Located at 2306 Massachusetts Ave. NW, the Barney is open to visitors Wednesdays and Thursdays by appointment (357-3111). The National Portrait Gallery Eighth and F Streets NW. 357-1300.

The National Portrait Gallery opened in 1968 in the south half of the old Patent Office Building. Dedicated to the exhibition and study of portraits depicting those presidents, politicians, writers, actors and others who contributed to the history, development and culture of the United States, the Portrait Gallery has had the difficult task of acquiring first- rate life portraits of and by great Americans. Gifts such as the collection of drawings for Time magazine covers will help future generations visualize the movers and shakers of mid-20th century America, but the past has remained a problem: great portraits of the nation's founders are an extreme rarity in today's market.

Solomonic solutions have helped the museum to build up the quality of its collection: the famous Gilbert Stuart life portraits of George and Martha Washington were purchased jointly with the Boston Museum of Fine Arts, and the paintings commute between the two museums; Stuart's "Edgehill" portrait of Thomas Jefferson, recently acquired, is owned jointly with Monticello. John Singleton Copley's self-portrait, however, is among the increasing number of fine portraits owned by the museum, which now also collects photographs. Incredibly, this was forbidden until a few years ago. The Hirshhorn Museum and Sculpture Garden Independence Avenue at Eighth Street SW. 357-1300.

The late uranium king Joe Hirshhorn who had a tough time getting Congress to accept his gift of 6,000 works that would establish -- in his name -- a national museum of modern art on the Mall. After a long and vituperative battle, the Hirshhorn Museum and Sculpture Garden finally opened in 1974 with paintings and with Hirshhorn's collection of 20th century sculpture, considered the finest in the world. At his death in 1981, he left the museum 6,000 additional works and an estimated $5 million.

The collection includes dozens of sculptures by Degas, Daumier, Picasso, Henry Moore and David Smith, along with some fine early American paintings by George Bellows and Thomas Eakins, whose portrait of his wife is one of the gems of the collection.

Larry Rivers' "History of the Russian Revolution" is a highlight of the contemporary collection, but works by virtually every major name in 20th century art turn up in changing installations. The Freer Gallery of Art 12th Street and Jefferson Drive SW. 357-1300.

Opened in 1923, the Freer and its treasures were a gift to the Smithsonian from Detroit industrialist Charles Lang Freer, one of America's first great collectors of Oriental art. Freer acquired 1,400 paintings by Winslow Homer, Thomas Wilmer Dewing, John Singer Sargent and James McNeill Whistler (including his famed "Peacock Room"), before Whistler convinced him that he should explore the art of the Orient.

The collection of 12,000 works from the Near and Far East that he subsequently formed -- including Chinese, Japanese and Korean scroll paintings, bronzes, ceramics and jade and manuscripts from Syria, Iran (Persia) and India -- is known worldwide for its extraordinary quality. The National Museum of African Art 318 A St. NE. 357-1300.

Founded by former foreign service officer Warren Robbins in 1964 as the only museum in the United States dedicated exclusively to the display and study of African art, this idealistic institution became part of the Smithsonian in 1979. Originally housed in half of the 19th century residence of abolitionist and publisher Frederick Douglass, the museum has now expanded to include nine connecting townhouses on Capitol Hill. Its collection of 8,000 objects has been vastly expanded by the gifts of no less than 350 donors, including photographer Eliot Elisofon. Sculpture from every art-producing area in Africa is now included, with a focus on wood carvings and bronzes from West and Central Africa. The museum also owns 250 paintings by 19th century Afro-American artists Henry O. Tanner, Robert S. Duncanson, Edward M. Bannister, Joshua Johnston and Edmonia Lewis. The Library of Congress First and East Capitol Streets. 287-5836.

Though known for other things, the Library of Congress contains a treasure trove of 70,000 works of graphic art dating from the 15th to the 20th centuries. It also has a growing collection of contemporary American prints and a thousands of photographs that document the entire history of the medium. All can be seen by appointment through the library's prints and photographs division. PRIVATE MUSEUMS The Corcoran Gallery of Art 17th Street and New York Avenue NW. 638-3211.

"The encouragement of the American genius" was what banker and American art collector William Wilson Corcoran had in mind when he founded the Corcoran Gallery of Art, the oldest art museum in Washington, surpassed in age in the nation only by New York's Metropolitan and the Boston Museum of Fine Arts. The museum opened in 1869 in what is now the Renwick Gallery and moved to its present Beaux Arts building in 1897.

The Corcoran is the only public art museum in Washington not supported by the U.S. government, nor -- to the city's shame -- by the District of Columbia, whose artists and citizens it serves. Again, private largess came to the rescue: philanthropist Armand Hammer made it possible two years ago for the Corcoran to abandon its entrance fee--the only one in Washington--and he and other donors, private and corporate, have brought the building's recent renovation and air conditioning to near completion.

The Corcoran's great collection of American art merits closer scrutiny than it has had from most Washingtonians. Starting with a Colonial portrait by John Smibert, one of America's first phizmongers, the collection boasts works by John Singleton Copley, Benjamin West, the Peales and inventor-painter Samuel F. B. Morse, whose "Old House of Representatives" must be worth at least $3,250,000, since another Morse painting of similar size but lesser quality recently sold for that amount.

There are also examples from the Hudson River School (notably Frederick Church's splendid "Niagara Falls"), the Ash Can School and the Washington Color School. The growing collection of contemporary art is among the best anywhere. The Phillips Collection 1600 21st St. NW. 387-0961.

If Washingtonians have one favorite museum, it is the Phillips Collection, the first museum of "modern art and its sources" ever established in America. Opened in 1918 in the red brick Victorian that Duncan and Marjorie Phillips called home before their collection forced them out, the museum has continued as a family affair. It is part of the magic of the place that it still feels like the home of truly great and passionate collectors.

The late Duncan Phillips, with his artist wife, believed profoundly in the new art that was coming from abroad early in this century, but thought American artists of vision needed support as well. Thus, in their quiet way, the Phillipses supported -- through extensive purchases (which they called "units")-- the work of American modernists like Milton Avery, Arthur Dove, Georgia O'Keeffe, John Marin and Mark Rothko, while continuing to acquire splendid "units" by C,ezanne, Bonnard, Klee, Vuillard and Braque.

Though some of the collection's greatest masterpieces (including Renoir's "Luncheon of the Boating Party") are currently touring other museums in an attempt to raise funds to supplement the museum's inflation-riddled treasury, there are still many wonders to see. Dumbarton Oaks 1703 32nd St. NW. 342-3200.

The Dumbarton Oaks Collection is a jewel nestled in Georgetown in a Federal-style mansion that once belonged to diplomat-philanthropist Robert Woods Bliss. Turned over to Harvard University in 1940 as part of a research center, the collection is displayed in two parts: Byzantine treasures, including precious and intricate ivories, gold jewelry, ecclesiastical silver and textile fragments dating from the fourth century are displayed in the main house; the Pre-Columbian collections are instanlled in eight sparkling glass pavilions designed by architect Philip Johnson that are set into the surrounding woods. Included here are works made in this hemisphere before the arrival of Columbus, notably Peruvian gold ornaments and textiles and Mexican stone sculpture and ceramics. Tapestries, furniture and paintings, including a small El Greco, are on display in the music room. The Textile Museum 2320 S St. NW. 667-0441.

George Hewitt Myers (of Bristol-Myers) was a passionate rug-collector; he founded this fine museum in 1925 in his former Kalorama home. Now a mecca for textile and rug aficionados, the museum's holdings include more than 10,000 textiles and 1,000 rugs, with preeminence in Near and Far Eastern rugs and one of the world's greatest collections of Pre-Columbian Peruvian textiles. The Museum of Modern Art of Latin America 201 18th St. NW. 789-3000.

One of the newest and least known of Washington's museums, this brave and hospitable institution has a fine and representative collection of works by the leading 20th century artists of Latin America. It is housed in a handsome former diplomatic residence behind Organization of American States building. On two floors can be seen some of the best-known names in contemporary art, including Orozco, Tamayo, Matta, Cuevas and Soto. Current trends are also represented in the work of artists not yet well known here. The museum was established by the OAS to mark the Bicentennial of the United States.