Any U.S. churchgoer who put 10-c- into the collection plate each and every Sunday of last year may warm his piety at the comforting thought that he was twice as generous as the average churchgoer. Authority for the fact that 5-c- is the average contribution, is the Federal Council of Churches of Christ in America, which published figures last week. The most generous State: New Jersey, 12.2-c- per churchgoer per Sunday. Virginia, the Carolinas, Washington and eleven other States averaged less than 5-c-.