The first of four men accused in a failed plan to build a biotechnology plant in Vermont using tens of millions of dollars in foreign investors’ money raised through a special visa program was sentenced Thursday to 18 months in prison. William Stenger, 73, the former president of the Jay Peak ski resort, also was sentenced to three years of supervisory release and ordered to pay $250,000 in restitution. He pleaded guilty last August to providing false documents. In exchange, nine fraud charges were dropped. Stenger told the court he wished to apologize to his family, the employees of Jay Peak and Burke ski resorts, the state, the investors, and his community of Newport.