Back in 1978, the Chicago Reporter, an investigative newsletter, conducted a ward-by-ward computer cross-check of Chicago parks and found massive evidence of racial discrimination. The study showed that parks in white areas had more and better facilities than those in black or Hispanic neighborhoods -- more skating rinks and tennis courts, more day camps and senior-citizen programs.

The Justice Department read the report, conducted its own 21/2-year study and, two weeks ago, filed the first-ever suit alleging violations of the 1974 Housing and Community Development Act, under which federal money is made available for municipal services, including recreation.

The suit is interesting in a number of ways. It was initiated by the Reagan administration, it seeks to enjoin the city from future discrimination, and it asks the court to order local officials to submit a plan to correct the effects of their discrimination. But what may be most interesting is that the suit is being hailed by minority spokesmen who would be aghast if the alleged discrimination involved public education rather than public recreation.

As in the case of unequal school facilities, Chicago officials deny "willful discrimination." It is a reasonable guess that if the court orders equalization of recreational facilities, and the city complies with the order, Chicago's two largest minorities will consider it a major victory. But if a similar order were handed down with regard to the city's public schools, civil rights leaders would almost certainly denounce it as a violation of the Constitution, a return to separate-but-equal.

I would be aghast, too, if the Justice Department had proposed that Chicago set aside certain parks for the exclusive use of whites, even if it asked for major improvements for parks set aside for the exclusive use of blacks and Hispanics. That is just the sort of racial segregation that resulted in the 1954 Brown desegregation decision.

But apparently people who find it altogether reasonable that parks and playgrounds should be used by people who happen to live near them (so long as there are no racial restrictions imposed on their use) find it outrageous when school assignments are made on the same basis. Suit after desegregation suit has been brought, not because schools serving black and white neighborhoods were unequal (though they often were) but because they were racially identifiable -- like Chicago's parks.

Schools and parks are different, of course, serving different purposes with different values. But the principles involved seem quite similar, and yet I find it impossible to imagine any Chicago civil- rights leader objecting to the Justice Department's recent action on the ground that it unconstitutionally promotes separate-but-equal parks, or that racially separate parks are inherently unequal.

Will someone please explain the constitutional difference?