Joseph Hirshhorn was particularly fond of little well-made sculptures, objects he could play with as kids play with their toys.

He was loyal to his favorites. When he made up his mind about an artist he believed in, he'd buy and keep on buying--he'd buy early works and late works, major works and minor ones (surprises gave him pleasure, oddities intrigued him)--until at last he'd mapped the artist's whole career. His tastes were catholic, he liked buying art from youngsters, and he always loved a bargain.

"Purchases by the Hirshhorn Museum, 1974-1983," which goes on view today, would have tickled Hirshhorn (1899-1981).

It is a mixed bag of a show. It includes some awesome objects--Aristide Maillol's monumental "Action in Chains" (1905-06), Richard Estes' "Waverly Place" (1980)--and more than a few clunkers. A number of its larger, ambitious abstract paintings, by Friedel Dzubas, for example, and by Jack Bush and Robert Motherwell, are a little bit embarrassing. A number of the pieces--the early and prophetic Stuart Davis "Gas Station" (1917), the rare Arthur Dove collage (one of only three he made), the early Kenneth Noland (1953)--are telling curiosities. And it's particularly rich in good, small-scale sculptures. It includes artists young and artists long dead, the famous and the unknown.

It is, in many ways, a baffling exhibit. Unless one knows in detail the Hirshhorn's permanent collection--and the gaps in that collection this art was bought to fill--it doesn't make a lot of sense. Nor does it display all the works of art with which the museum has gradually augmented its original collection. It includes only purchases. But the 157 works bought by the museum (all but 10 are in this show) are outnumbered more than 8-to-1 by the 1,282 it has received as gifts.

The museum, since its opening, has spent approximately $3.3 million buying works of art. By modern market standards, the collection on display was relatively cheap. This, too, would have pleased Hirshhorn.

Nearly half that sum--about $1.5 million--was spent on just four objects, all of which were purchased with the aid of a special Smithsonian program for major acquisitions: More than $200,000 went in 1981 for a new cast of "Standing Woman," a 1932 bronze by Gaston Lachaise; the even larger Maillol, another posthumous casting, cost more than $350,000 in 1979; "Cylinder Decorated With the Figure of Hina and Two Attendants," a rare 1892 woodcarving by Paul Gauguin, cost more than $400,000 in 1981; and, in 1980, approximately $500,000 went for "Woman Before an Eclipse With Her Hair Disheveled by the Wind," a large 1967 canvas by Joan Miro'.

All the other objects here were bought for a total of only $1.8 million. These include works by Max Beckmann, Anthony Caro, Joseph Cornell, Richard Diebenkorn, Jim Dine, Honore' Daumier, Ron Davis, Stuart Davis, Willem de Kooning, Thomas Eakins, Helen Frankenthaler, Gregory Gillespie, Adolph Gottlieb, Al Held, David Hockney, Louis Lozowick, Robert Motherwell, Claes Oldenburg, Jules Olitski, Auguste Rodin, Tony Smith and David Smith, Frank Stella, Wayne Thiebaud and John Butler Yeats.

Given today's prices for works by famous artists, that is not a lot of money. If one excludes the Lachaise and the Maillol, the Gauguin and the Miro', the other 153 objects bought by the museum cost, on average, about $12,000 apiece.

Some of them are grand. The Cornell box, the major Tony Smith, the extraordinary Estes, the early and impressive Frankenthaler abstraction, the memorable Lozowick, the Thiebaud, and the "Geometric Mouse" by Oldenburg are all impressive works of art. A few of them are vapid. Two David Smiths, both paintings, are weak. The Dzubas "Early Gray" (1966) is weaker. And Motherwell's "Elegy to the Spanish Republic #129" (1974), although it strives for boldness, has in it something tired, as if he's been too long copying himself.

The show includes nine objects made in Washington--by Peter de Anna, Sam Gilliam, Lois Mailou Jones, Jacob Kainen, Kevin MacDonald, Kenneth Noland, Anne Truitt and the late Alma Thomas. "Interface 5," Kainen's 1982 rectilinear abstraction, was purchased, rather touchingly, with monies from the "Fountain Fund"--with nickels, dimes and quarters retrieved from the museum's pools.

The 19th-century sculptures here--the medallions by Auguste Pre'ault, the plaster study by Carpeaux, and two bronzes by Aime'-Jules Dalou--are particularly impressive. Also encouraging are a number of strong figurative pictures by far-from-famous living artists--"Edge of the City With Beltway" by Robert Birmelin (1978-81), "Sprowl Brothers Lumber Yard, Searsmont, Maine" by Rackstraw Downes (1979-80), "Man Seated in an Interior" (1977) by the Spaniard Oscar Mun oz, and "Two Figures in the Corner of a Room" (1978-79) by England's William Wilkins.

A number of the objects here--"Waverly Place," the Lozowick, the Thiebaud, and "Myself Painting a Self-Portrait" by Gregory Gillespie--have proved extremely popular. It is easy to see why. "Purchases by the Hirshhorn Museum, 1974-1983" closes Nov. 13.