AFTER a decade of relative calm, sex education appears to be in for a new round of assault. Recent months have witnessed numerous signs of renewed anti-sex-education sentiment. George F. Will has criticized sex education in his nationally syndicated news column; Ronald Reagan has assailed sex education on his syndicated radio show; Senator Jesse Helms has criticized sex education on the floor of the U.S. Senate; ABC-TV has televised a debate on sex education on its Good Morning America; and reporters for both CBS-TV’s 60 Minutes and the National Enquirer have begun investigations of selected sex-education programs.