Heat oven to 350°F. Grease 15x10x1-inch baking pan. In medium saucepan, combine chocolate chips, 2 tablespoons margarine and sweetened condensed milk. Cook over low heat until chocolate is melted and mixture is smooth, stirring constantly. Set aside.
Melt 1 cup margarine in large saucepan; remove from heat. Add brown sugar and eggs; blend well. Lightly spoon flour into measuring cup; level off. Add flour, coconut, pecans, salt and vanilla; mix well. Spread half of batter in greased pan. Drop chocolate mixture by tablespoonfuls over batter; carefully spread to cover. Drop remaining batter by teaspoonfuls over chocolate mixture; swirl slightly with tip of knife to marble mixture.
Bake at 350°F. for 25 to 35 minutes or until light golden brown and center is set. Cool; cut into bars.