The death toll among celebrities over the long President's Day weekend was unusually high. Among them: Balthasar Klossowski, 92, the artist known around the world as BALTHUS, died on Sunday at his chalet in Switzerland, having over his lifetime excelled as a portraitist, a painter of landscapes and someone who redefined the notion of Parisian townscape . . . Animal welfare advocate ROGER CARAS, 72, a former president of the ASPCA and the announcer of the Westminster Kennel Club Show (which last week took place at New York's Madison Square Garden without him for the first time in year), died on Sunday of a heart attack he had suffered in December, his daughter told The New York Times . . . Designer MORISON S. COUSINS, 66, who revamped the look of Tupperware, died on colon cancer on Feb. 10, his family announced this weekend. His European designs gave a spiffy new look to the down-home product, and Cousins's design (he joined Tupperware in 1990) found their way into museums around the globe . . . "Mannix" actress Gail Fisher, 65, who won a 1970 Emmy for her portrayal of secretary Peggy Fair on the detective series, died of kidney failure on Dec. 2, it has just been reported. Fisher was one of the first African Americans to play a major serious role on TV . . . Author FRANK GILBRETH JR., 89, whose 1949 "Cheaper By Dozen" (which a year later was turned into a memorable movie with Clifton Webb and Myrna Loy), died on Sunday in South Carolina, where he'd lived for the past half-century. Gilbreth wrote about his efficiency expert old man and how he applied his expertise to his household, which consisted of six sons and six daughters . . . Pioneer "sexpert" WILLIAM H. MASTERS, 85, who with his co-researcher, Virginia E. Johnson, revolutionized the way sex is studied, taught and practiced in America, died Friday at a hospice in Tucson . . . Baseball Hall of Famer EDDIE MATTHEWS, 69, the Atlanta Braves third baseman who hit 512 home runs and teamed with Hank Aaron to form the most power-hitting combo in the history of the game, died of complications of pneumonia on Sunday . . . and French pop singer CHARLES TRENET, 87, known to Americans for his trans-Atlantic hits "Beyond the Sea" and "I Wish You Love," died in Paris on Sunday. Singer Charles Aznavour said of Trenet, "Thanks to him, the public discovered surrealism in song."