In a large saucepan, saute onions in margarine. Stir in flour, chili powder, and cumin. Add corn, picante sauce, and broth. Bring to boil; remove from heat.
Gradually add 1/4 cup hot mixture to cream cheese in a small bowl. Stir until blended.
Add cream cheese mixture and milk to saucepan, stirring until well blended. Heat through but do not boil. Serve immediately.