SIX YEARS ago, the District of Columbia enacted a law providing a fixed quota of city construction contracts to minority contractors. Does that not seem fair and reasonable? But some of the minorities soon concluded that too many minorities had been included. In 1980, the city amended the law to exclude the Asians, as well as those Hispanics who actually came from Spain. It was felt that those people had not been adequately discriminated against, over the years, to entitle them to preference for city contracts. To be a Hispanic from Argentina or Chile was sufficient indication of having been wronged, the council held, but to be a Hispanic from Spain was not.

This interesting change in the law became an issue in the recent city election. Spanish-American and Asian contracting interests put some money into Mayor Barry's campaign, and extracted from him a promise to sign legislation restoring them to the list. As it now stands, the recognized minorities, for purposes of the contract quota, are blacks, native Americans, Asian American, Americans who trace their ancestry to the Pacific islands, Hispanics who don't come from Spain and Hispanics who do come from Spain.

But since he signed the latest amendment to the previous amendment, Mayor Barry has been hearing from black contractors. He has now come to believe that the imperatives of social conscience would be better served if the Asians and the Hispanics from Spain were kicked off the list again.

The quota for minorities was originally 25 percent of all contracts, but has now crept up to 35 percent. The solution is obvious, if you want to follow the logic that has got us where we already are: the city council could best expand the quota for minorities to 100 percent of te city's contracts, and lengthen the list of protected minorities to include all of them--black, white, yellow and brown, including all those who trace their anthropological origins to areas east of the International Date Line, as well as those west of it.

That would produce a public policy that is intellectually respectable, consistent and free of any taint of either racial discrimination or the pork barrel. That's more than you can say about the present law, with or without Mayor Barry's latest amendment.