Bring first 4 ingredients to boil in large saucepan on medium-high heat, stirring occasionally. Meanwhile, mix meat, rice, bread crumbs, egg and cheese; shape into 16 (2-inch) meatballs.
Add meatballs to tomato mixture; stir. Cover; simmer on medium-low heat 30 min. or until meatballs are done (160F), stirring occasionally.
Remove about 1/2 cup of the sauce; mix with sour cream. Return to pan; stir until blended.