Australia would damage its defense alliance with the United States if Canberra quits Iraq, Prime Minister John Howard warned critics Monday. Howard said he had agreed to send 2,000 troops to back the US and British militaries in the Iraq invasion due to the perceived threat of weapons of mass destruction - but also to preserve Canberra's alliance with Washington, formalized in a 1951 security treaty. "We ... took the decision in part because of our alliance with the United States," Howard told Southern Cross Broadcasting radio. "I have to now deal with a decision," Howard said. "Do we rat on the Americans?"