A team of American and Filipino biologists has discovered a new species -- or perhaps a new genus -- of mouse in the Philippines that took them quite by surprise. The tiny mouse was captured on Mount Banahaw, a national park in the south-central portion of Luzon Island, only about 50 miles from Manila. The bright-orange animal has a large head, heavily muscled jaws and powerful teeth that can open hard nuts. It weighs about 15 grams, and has a body length of 3 inches and a tail of four inches. The mammal's whiskers are about eight times as wide as its head, and there is a second set of ''whiskers'' that arise from a patch at the back edge of each eye.