DES MOINES — Representative Ron Paul of Texas assailed criticism of his opposition to United States military involvement abroad, saying he fears an overreaction to worries about Iran’s nuclear program could lead to war.

Mr. Paul’s rivals have hammered him for days as too dovish and suggested that he would do nothing to prevent Iran from acquiring a nuclear weapon. Mitt Romney again criticized Mr. Paul on Friday in an interview on the Fox News Channel, saying, “I don’t think Ron Paul represents the mainstream of Republican thought with regards to issues, particularly in foreign policy.”

Mr. Romney and other Republican candidates have said they would take military action if economic, diplomatic and other pressure did not prevent Iran from building a nuclear device, warning that Tehran could launch a first-strike nuclear attack on Israel.

Mr. Paul, though, stuck to his guns. Before a crowd at a public library in Sioux Center, he noted that others say Iran “might get a nuclear weapon someday, and wouldn’t it be good if we have a pre-emptive attack on Iran right now to make sure they never got a weapon.”