Detroit Country Day in Beverly Hills, Mich., may be a pricey private school, but its administrators say they shouldn't have to spend money to put in a block or so of sidewalk. After months of negotiations with village officials broke down two weeks ago, the school filed legal documents in Oakland County Circuit Court seeking a judge's opinion on the matter. Cost estimates for sidewalks were $150,000. The dispute began last spring, when Country Day began building a new gymnasium. Under the village zoning ordinances, the development required the installation of a sidewalk.