The Emmis Broadcasting Corporation said yesterday that it would buy four television stations from a Fox-USA Broadcasting Inc. venture and two other stations for a total of $397 million. Emmis said it would pay SF Broadcasting, the Fox-USA venture, $307 million for all four of its stations, including $257 million in cash and $50 million either in cash or Emmis class A stock. It will also pay Wabash Valley Broadcasting $90 million for the other two stations. The four SF Broadcasting stations are KHON-TV in Honolulu; WVUE-TV in New Orleans; WALA-TV in Mobile, Ala., and WLUK-TV in Green Bay, Wis. The two Wabash Valley stations are WTHI-TV in Terre Haute, Ind., and WFTX-TV in Fort Myers, Fla. Shares of Emmis gained $2.875, to $52.75.