Mayor Giuliani yesterday said he would find it hard to back any Republican presidential candidate who favors repealing the federal assault-weapons ban, further distancing himself from GOP front-runner Robert Dole. "There should be very, very few litmus tests, but someone who now voted to roll back the assault-weapons ban would really be demonstrating that special interest politics mean more to them than life-or-death issues," said Giuliani, who irked GOP leaders by appearing with President Clinton to support the gun legislation. Giuliani said he would consider candidates' overall presidential platforms, but he said their position on the ban "should bear very,...