Heat 10-inch nonstick skillet over medium heat. Add butter, flour, cumin and garlic; beat with whisk to mix. Cook 3 to 4 minutes or until very fragrant. Beat in milk; heat to boiling. Cook, beating constantly, until thickened.
Remove skillet from heat. Add cheeses; beat until melted. Stir in tomatoes, green onions, cilantro and green chiles. Serve dip immediately with chips.