Major League Baseball is working on a scheduling reconfiguration beginning next season that likely will eliminate the Mets and Yankees as well as other "natural rivals," according to sources. With the Astros moving to the American League West next season and the leagues becoming balanced at 15 teams apiece, natural rivals throughout baseball no longer will be guaranteed six games a season and home-and-home series. That goes for obvious inner-city rivals such as Mets-Yankees and Cubs-White Sox, as well as for more-forced natural rivals such as the Padres and Mariners.