Preheat oven to 325°.
Bring water to boil in heavy, medium saucepan.
Add butter and salt.
Mix in rice.
Reduce heat to low, cover and cook until rice is tender, about 25 minutes.
Transfer to large bowl and cool, fluffing occasionally with fork.
Butter an 8 cup shallow baking dish.
Heat vegetable oil in heavy medium skillet over medium heat.
Add onion and garlic and saute until onion is translucent, about 5 to 6 minutes.
Add chopped chiles and saute one minute.
Mix chile mixture and corn into rice.
Combine sour cream and cilantro in small bowl.
Add to rice and mix well.
Stir in cheese.
Transfer rice mixture to prepared dish.
Bake about 25 minutes or until sides are light brown and mixture is heated through.
Can be prepared one day ahead.
Refrigerate.
Let stand one hour at room temperature before cooking.