Preheat oven to 350°F. Grease a 13" x 9" metal baking pan. Line with foil and grease foil.
In heavy 3 qt. saucepan, melt margarine over low heat. Remove from heat; stir in brown sugar and vanilla. Stir in eggs. Combine dry ingredients and stir into sugar mixture, just until blended. Add pecans. Spread evenly in pan.
Bake 30 minutes. Test with a toothpick 2" in from edge; should be clean (do not over bake). Cool completely; cut into 24 bars.