The government today appears a champion of the arts - what with Joan Mondale traveling the country, and the National Endowments pouring millions into culture, and the National Gallery's East Building newly open on the Mall - but it has not been one for long. That point is made, and nicely, too, by "Past and Present: A Century and a Half of a National Collection," which will be on view all summer at the National Collection of Fine and Arts (NCFA).

It is not a show of "treasures, nor was it meant to be. Instead, it shows clearly how timid and how fitful has been the U.S. government's patronage of art.

There is a telling photography near the end of the exhibit. It was taken in the 1920s and shows the director of the newly established "National Gallery of Art" (as it then was called; it is now the National Collection) and his staff of - count them - three.

The NCFA is the least pretentious of this city's art museums. Its "chief aim" writes Joshua C. Taylor, its director. "is to open up new avenues of thought regarding American art, often through the examination of little recognized aspects of art." The aspect explored here - with 200 works of art, mostly rescued from the attic, a number of them gems, a few quite ugly - is the complex story of the gradual development of a national collection in the United States.

That story might as well begin in 1829 when, writes Taylor, "John Varden, a man apparently of no great culture but of considerable initiatives" set out to assemble works to be displayed in his "Washington Musueum." "At least two works of art survive from his collection, both of which attest to his belief in old varnish and [WORD ILLEGIBLE] condition as marks of [WORD ILLEGIBLE] city. One was a violent Italian painting, 'Massacre of the Innocents,' which he hoped was by Raphael." It wasn't. (For most of the next century, the national collection would remain enormously ambitious in its attributions.) (The "Massacre," now given to an "unidentified artist," is nevertheless included in this show.)

"Past and present" celebrates a pair of anniversaries, one a tenth, the other a 149th. Though it has been 149 years since Varden started buying works of art, it has been only 10 since the National Collection of Fine Arts moved into the Old Patent Office Building, 8th and G Streets NW, the first museum of its own.

Between 1829 and the 1960s, the government's art collection just sort of bumped along. It grew, but not by plan. It was moved from place to place (and much of it was lost when fire swept the Smithsonian Institution's "castle" in 1865). "The fire has a retarding effect on the institution's none-too-avid interest in building collections," writes Taylor. "The regents for some years rather hoped that William Corcoran's gallery . . . would relieve them of the necessity of carrying out their mandate to include art in the Smithsonian's range of fields."

But gifts from public donors - Harriet LaneJohnson, William T. Evans and John Gellatly, prominent among them - were nonetheless accepted.Many are on view.

These include a bust of President Van Buren (Harriet Johnson's uncle), and a bronze statue of Daikoku, the Japanese god of plenty (viewers seeking luck often have put pennies into Daikoku's open, laughing mouth). A number of fine pictures also were accepted, some of them European (one a fine Guercino), but more of them American. Thanks in large part to Evans and Gellatly, such American masters as Mary Cassatt, Winslow Homer and Albert Pinkham Ryder have long been represented in the NCFA.

Works also were received from other branches of the government, among them a small plaster of Bartholdi's "Liberty," which was given to the U.S. Capitol, but did not stay there long. The bird people at the Smithsonian parted with some of Audubons. And many various pictures, a number of them fine, came from federal art projects such as the WPA.

By coincidence this show in some ways resembles the Dresden exhibition at the National Gallery. This show is much less grand, and much more provincial, but it, too, is well-installed (Val Lewton did the installation), and both shows take the viewer through changing tastes and changing times.

The Varden museum was a kind of Kunstammer, or cabinet of curiosities (there were only 30 paintings among its 400 or 500 objects). Both the American and Dresden shows reflect the nation's wars. There are some military portraits, and a number of French drawings given to the United States by French artists who were grateful for our aid in World War I. But what ties these shows together is their sense of marching time.

Here we see the genteel taste of the 1890s (for instance, the lovely works by Thomas Wilmer Dewing), and the gropings toward the modern of the 1930s, the streamlined style of the '40s and much '60s art. There are surprises. Did William Zorach predict the style of O'Keeffe, before World War I? Did Francis Criss in 1934 predict later Edward Hoppers? And why have we not heard more of the haunting pictures of O. Luis Guglielmi?

This show includes delights, Frank Blackwell Mayer's "Independence," that silver point by Dewing, and Harry Siddons Mowbray's scene of two bored beauties watching turtles feed. These painters, although fine, do not have names quite big enough to warrant their inclusion in the National Galllery.

That is the nicest thing about this show and the National Collection. It doest not try to edit, or to sugarcoat, the history of art. Instead it shows oddities - a tiny teacup carved of emerald, an Ilya Bolotowski picture of a barbershop made before that painter discovered Mondrian, and a Childe Hassam portrait of a woman potting roses which is, by any standards, ugly, though it does have a nice frame.

Washington today seems a city of museums. Those who like to brag about the city's art collections, and its connoisseurship, ought to see this telling, often humbling show. It will be on view through Sept. 4