ONCE UPON A TIME the American working man would proudly take along the tools of his trade when he went to sit for a formal portrait. So would the working woman, who would face the tintypist with shuttle or scuttle in hand.

There is dignity and determination in these faces, now gazing at visitors to the Museum of American History's new exhibit, "Symbols and Images of American Labor." It is a way of life all but unimaginable in the era of electronics and automation.

In the old days each trade had its distinctive badge, cap or coat. Be he butcher or baker or candlestick maker, a man's occupation and status could be read at a glance. These days, the man in the street -- or in the fern bar -- could be a secretary or a steelworker, who can tell?

On patriotic occasions platoons of artisans would parade in the regalia of "mechanics" societies: chairmakers, glasscutters, ropemakers, cabinetmakers, saddlers, stablemen, hodcarriers, granite miners . . . At the turn of the century, the United Mine Workers of America issued poster-size membership certificates with idealized scenes of miners at work under the motto, Labor As Wide As The Earth Has Its Summit In Heaven. Mill girls published literary magazines. Trade unions sponsored lectures on science.

But industrial workers gradually became interchangeable attendants of automatic machines owned by ever more remote capitalists ("Oh, they don't feel pain, they don't even speak English"). As the skill went out of the work, so did much of the pride. Down went the upbeat Knights of Labor, up came the two-fisted Wobblies (Industrial Workers of the World), who dreamed of a future in which One Big Union would own all industry, and issued a little red book called Songs to Fan the Flames of Discontent.

Pride of craft and a sense of the worth of manual labor can be counted among the casualties of the labor struggle. Many of us mumble when asked what we do for a living. We're still a long way from a classless society, but we have lost a lot of our class.

SYMBOLS AND IMAGES OF AMERICAN LABOR --

Through July at the National Museum of American History.