Ben Shahn should have been there. The tough old crusader, who used his pencil, paints and brushes as weapons for progressive causes, would have been right at home at the opening of the "Images of Labor" show, on exhibit through Aug. 27 at the National Museum of American History. Shahn died a dozen years ago, but his spirit broods over the collection of 32 paintings, collages and sculptures commissioned by a hospital workers' union.

The fusion of word and image -- Shahn's specialty -- is the show's basic approach. District 1199 of the National Union of Hospital and Health Care Employees selected quotations from sources ranging from the Book of Job ("Man is born to labor and the bird fo fly") to Merle Travis ("I owe my soul to the company store"), sent them to selected artists with a modest commission and organized the results into an exhibit with strong impact. The show, which opened Friday, will tour in the United States and overseas for several years under the auspices of the Smithsonian Institution Traveling Exhibit Service.

The average quality of the works is considerably better than the sponsors had any right to expect. It is basically poster art, but poster art at its highest levels. The power in Edward Sorel's illustration of a quote from a mine operator, "They don't suffer; they can't even speak English," probably comes closest to Shahn's impact. But there is a similar strength in Sue Coe's "Strike," with its image of factory workers standing next to their idle machines, and in May Stevens' illustration of a feminist quote from Lucy Parsons: "We are the slaves of slaves. We are exploited more ruthlessly than men."

Personalities are as important in the show as ideas and slogans -- notably Audrey Flack's quietly heroic portrait of Sojourner Truth, linked to a quote from the famous speech that made her a living embodiment of two liberation movements, for black people and for women. Samuel Gompers looks out, stern but benign, from a ceramic mask by Robert Maeson. Abraham Lincoln, in perhaps the most controversial piece in the show, looks a little bit like a giant grasshopper -- but William King's sculpture is also immediately recognizable as Lincoln.

In some cases, the image and words fuse into a unit that functions more as propaganda than as art but is still effective -- for example, James McMullan's portrait of Joe Hill, linked to the last words he wrote before facing a firing squad in the Utah State Prison: "Could you arrange to have my body hauled to the state line to be buried? I don't want to be found dead in Utah."

The serious, message-laden exhibit has its moments of lightness. Honore Sharrer's illustration of the "trickle-down" theory of economics use a cartoon sort of vocabulary with elegant wit. Ralph Fasanella takes time, in his neo-primitive New York street scene, to poke fun at Andy Warhol with a can of beans in the lower right corner. There is pathos, too, in some pieces that could stand as absolute works of art without any propaganda overtones. John Collier's haunting picture of a tired young millworker and Daniel Maffia's illustration of the Knights of Labor motto, "An injury to one is an injury to all," may be the most impressive works in the show.

Naturally, the quality is variable. It is at its worst, perhaps, in Judy Chicago's contribution -- the usual Judy Chicago painting, with no perceptible relation to its supposed subject. Philip Hays' painting of three hard hats is an interesting abstract design, but it is hard to imagine why it was put on the cover of the (generally excellent) book prepared for the exhibit. Barbara Nessim's unraveling American flag is an uninteresting variation on a tired idea, and Robert Grossman's illustration of a verse from "Sixteen Tons" has nothing like the power of the song. But these are small blemishes in a show whose interest is specialized but very strong.