There is a shop in Springfield, Ill., where some grownups trade votes with less integrity than children trade baseball cards.

This shop is not a whole lot different from the others in the chain of state capitals. Many of the employees of the people, calling themselves representatives, spend their days playing swapping games with each other.

They call it legislating. They call it playing "hardball." Or horsetrading.

But last week, the Springfield shop gave a classic example, a minidrama that showed in the clearest terms how the Equal Rights Amendment has been dealt with. As if it's just another nag.

Last Wednesday, the ERA came up for vote in the Illinois House of Representatives. Twice before, in that bargaining hall, it had won a simple majority of the votes. Once it had won the necessary three-fifths majority, only to be bottled up in committee. But this time, the ERA supporters - a cautious group who learned the hard way from years of idealistic naivete - thought they had the votes, perhaps even a path through the Senate.

But a funny thing happened. A funny thing often happens during an ERA vote, whether it's in Tallahassee or Raleigh or Springfield. Surprises and problems pop up like clowns out of a circus car. Every time you're sure the car is empty, another clown coms out.

This time, when the votes were called, five black representatives from Chicago. ERA supporters from roll calls back, withheld their votes. They were in a snit against their own party for not consulting them on an issue of black leadership. So, angry and slighted, the Chicago Five, as Rep. Alan Greiman said, "stood there and let it go down without saying a word."

Later the five were not so silent. They issued the most bizarre press release ever to deserve a place in the psychological library of American history. "Today," it said, "several members of the Illinois legislative black caucus faced a very difficult choice, much like Kunta Kinte. They were asked to . . . ratify a purported deal to deliver the black vote and lose their manhood, or . . . lose a foot and not support the ERA forces."

Without the slightest hesitation, they asserted their "manhood" by denying women their equality. Without the slightest hesitation, they traded away decades of American history and the rights of half the population in order to protest an internal party squabble.

A fleeting principle of male pride came before a constitutional principle of female equality.

Perhaps it should have been expected. The ERA vote has hung on every irrelevant issue from a band marching in the inaugural parade, to a state ethics investigation, to a religious endorsement. If it is stalled three states short of victory, it's not because of backlash or the New Conservatism, or all the other trendy little things.

The amendment has been the victim of uninterest, hostility and fear toward women's rights. It's been held back by a dozen men in a few states who consider it a tradable commodity.

The pro-ERA forces in Illinois have regrouped and introduced another resolution. There is a small chance that it will come up for a vote again this month. The supporters hope that the pride of the Chicago Five can be appeased. They hope to hold together the chewing-gum coalition of votes massed for last Wednesday's assault.

But while that is being decided in the Springfield shop this week, the issue will come up in another way in Washington. The bill to extend the ERA deadline from March 1979 to March 1986 has been sent to the House Judiciary Committee. There's no piece of evidence that supports its passage more solidly than the Springfield saga.

After watching that piece of bartering, the need for extension is obvious. We need it because, as Liz Carpenter, co-chairman of ERAmerica said, getting 38 states before next March "is going to be a cliffhanger, and human justice shouldn't be a cliffhanger."

And we need it to remind state legislatiors that equality isn't a Babe Ruth card that can be so cavalierly traded for pride or prejudice.