Tempers were hot and separate sets of roadblocks kept outsiders away from the St. Regis Indian Reservation in Upstate New York, where federal and state authorities had raided four gambling casinos earlier last week. About 50 state troopers sealed the area around the reservation, which straddles the Canadian border near Hogansburg, and Mohawk Indians closed the roads within the 14,460-acre territory for a third day. “We’re detouring traffic around the reservation because they’ve shut down the roads inside,” said State Police Sgt. Michael Downs. Tribal chiefs, who have written to Gov. Mario M. Cuomo calling the dawn raid Thursday an “act of war,” meanwhile agreed to hold a referendum this week on whether the reservation should continue to sponsor gambling activities.