In 4 qt microwave casserole, combine potato, leeks or onions, celery, carrot, and margarine;cover with plastic wrap and zap on high for 6 min, until potato is softened. Add tomatoes with liquid and thyme, recover with plastic wrap and zap again on high for 5 min until potato is soft and mixture is thoroughly heated. Arrange clams hinge side out and cover again...Zap 3 min turn... Zap 3 min.Let stand 5 min and serve.