Chan. 21 readiedBackers of a new commercial television for New Hampshire say they may begin building their transmitter within a month or two.Former Gov. Hugh Gregg of Nashua, one of the partners pushing the station, said the Federal Communications Commission on Friday issued a construction permit.The transmitter will be built atop Fort Mountain in Epsom, Gregg said. The studios are to be built in theConcord area, he said.Other partners in the venture are James E. Chandler of Amherst, Delcie D. Bean of Dublin, John S. Gikas of Manchester and Richard F. Hartnett of Hamilton, Mass., a broadcast executive with New Hampshire interests.The station, to be assigned channel 21, is planned to cover the Lakes Region to the Massachusetts border andKeene to the Seacoast.Plans call for the station to operate independently, broadcasting news and public service events. Its editorialence.Officials expect to get the station on the air late this year or early in 1982.