Rock Hudson is sitting up in bed and getting better every day, his publicist said yesterday. The 59-year-old actor remained in fair condition at UCLA Medical Center, and doctors said they may allow him to have visitors next week. Among those who have called him are Jane Wyman, Lillian Gish, Elizabeth Taylor, Carol Burnett, Roddy McDowall and Ricardo Montalban.

Jazz singer Sarah Vaughan, who performed at Blues Alley last week, got her own star on Hollywood's Walk of Fame Wednesday. Los Angeles Mayor Tom Bradley was there to declare "Sarah Vaughan Day," in recognition of her 40-year career . . .

If you happen to be down along the Potomac today and see a happy group of grocery store executives, it's because they are having lunch aboard the Diplomat with Pauline Porizkova, who is the body in the humorous Diet Sprite television commercial and is so well remembered from Sports Illustrated's swimsuit issues. She'll be on the boat helping to sell the diet soft drink, so look for bigger stacks of the stuff on supermarket shelves . . .

Singer Tom Jones really works up an appetite, and after his performances at the Kennedy Center Tuesday and Wednesday nights he ate his way through a substantial portion of the menu at Jean-Louis, the very expensive Watergate eatery. He was there until 3 a.m. yesterday eating red and yellow sweet pepper soup garnished with crab and seaweed, noodles with slivers of codfish and herbed ravioli, and Maine lobster with corn mousseline. The main course was loin of baby (bunny) rabbit with shallots. He did limit himself to one dessert, a raspberry souffle', cognac and a cigar. He must be slowing down -- the previous night he had two desserts . . .

Former Georgetown University basketball star Patrick Ewing will celebrate his 22nd birthday next week with Jamaica's Prime Minister Edward Seaga during Ewing's first visit to his homeland in nine years . . .