Lawyers for Yonkers headed for another showdown over a bitterly contested court-ordered desegregation plan, insisting the city is not required to choose an alternative to a disputed low-income housing site. The move prompted Yonkers Mayor Nicholas Wasicsko to warn that the action could trigger U.S. District Judge Leonard Sand to reinstate crippling fines. Under a consent decree, the city agreed to build 200 units of low-income housing on seven sites in predominantly white areas, including one owned by the Roman Catholic archdiocese of New York. The archdiocese filed suit to prevent construction of public housing on church property and an appeals court has returned the case to Sand for review. In court papers filed with Sand, city corporation counsel Paul Pickelle argued that Yonkers was not required to provide an alternative site for the housing until a hearing was held.