Swathed in Balenciaga, Sarah Jessica Parker proved that a pregnant star needn't sacrifice style to hide her bulge from viewers. And now her sitcom colleagues will try to follow her lead. Though Courteney Cox Arquette and Curb Your Enthusiasm's Cheryl Hines aren't shooting during their big-bellied months, King of Queens' Leah Remini and Will & Grace's Debra Messing (above with Geena Davis) will model the latest in giant purses and loose tops. ''We want to keep Grace as chic as possible,'' says costumer Lori Eskowitz-Carter. Over in Queens, where style is relative, says a rep, ''[Leah] will probably stand behind lots of couches.''