Former Vice President Dan Quayle, hospitalized over the weekend for a dangerous blood clot in his lung, underwent treatment today in Indianapolis just weeks before he was expected to announce apossible 1996 presidential bid. Quayle, 47, went to the emergency room for a chest X-ray Sunday and was diagnosed with walking pneumonia. Such clots, called pulmonary embolisms, start in the calf of a leg and work their way up the body to become lodged in the pulmonary vein of one of the lungs. (Of up to 700,000 people a year affected, 5 to 10 percent die suddenly.)Quayleis expected to recover fully. If he's otherwise healthy, chances are "he would never have another one," his doctor says.Post your opinion on theHealth & Medecinebulletin board.