Vietnam’s wild elephant population faces certain extinction unless action is taken to protect the animals, according to a study released yesterday by Fauna and Flora International, a British conservation group. Between 98 and 150 wild elephants now live in the nation’s fragmented forests, down from an estimated 1,500 to 2,000 in 1990. Though poaching for ivory has been a problem, the main concern is loss of habitat: Half of the 100,000 acres of the elephant’s native forests in Vietnam’s two southern provinces were converted to agricultural land from 1992 to 1998.