WASHINGTON - Women are about to get their first chewable birth-control pill. The Food and Drug Administration on Friday approved a chewable, spearmint-flavored version of a contraceptive tablet called Ovcon 35. A woman can either swallow the pill whole or chew it, as long as she then drinks a full glass of liquid immediately afterward to ensure that the full dose reaches the stomach and no residue is left in the mouth, the FDA said. Warner Chilcott Inc. of Rockaway, N.J., will market the chewable contraceptive. The company has not announced when the pill will go on sale.