The debate also brought an angry response from Allen when a panelist asked him whether the word he applied to a Webb campaign volunteer of Indian descent, "Macaca," was a racist slur he had learned from his French Tunisian mother.
Allen criticized Webb for saying in Sunday morning's debate on NBC's "Meet The Press" that Iran and Syria needed to be brought into a multinational effort to end the sectarian bloodshed in Iraq.
"It doesn't make much sense to me to have a country like Iran, which is clearly a state sponsor of terror ... to have them forming the future of Iraq," Allen said during the Fairfax Chamber of Commerce debate.
Allen said the issue of involving adversaries in the region in a settlement is the only significant difference between himself and Webb.
But Webb, an outspoken opponent of the 2003 Iraq invasion, said he and Allen differed profoundly, particularly on stationing U.S. troops indefinitely in Iraq.
"We've been divided from Day One — whether we should have gone in, which I believe was a strategic error," said Webb, who left the Republican Party partly because of the invasion that Webb says destabilized the region and strengthened Iran's hand.
"If you go to how we solved the problem in Afghanistan, one of the reasons it was so successful is we brought all the countries around Afghanistan ... to the table, including Iran," Webb said. "The problem with this administration is it has blinders on on this issue."