All the tough problems of U.S. North ern school integration the ironies of good intentions and painful misunder standings, the subtleties of trying to ig nore skin color while trying to take it into account, the vain hope of having schools that serve both slums and middle-class neighborhoods welled up last week in New York City's Harlem.Looking back, there is not much doubt that New York City's Board of Education should have built its new In termediate School 201 somewhere else than right in the middle of darkest East Harlem.