DES MOINES, July 28 — Senator Barack Obama, who has spent the first six months of his presidential campaign focusing on his own attributes, has found a new anecdote in his quest to convince Democrats that he is a fresh voice of change: his foreign policy dust-up with Senator Hillary Rodham Clinton.

For days, Mr. Obama and Mrs. Clinton have been exchanging retorts over the wisdom of sitting down for diplomatic meetings with hostile dictators. In case voters had not been following along, Mr. Obama sought to inform them, weaving his side of the dispute into the overarching message of his campaign.

“Some of you noticed that this week I got in a debate with one of my colleagues who is also running for the presidency,” Mr. Obama said Friday night, opening a two-day trip to Iowa. “The debate was about whether we talk to world leaders even if you don’t like them. My theory is that you do.”

The quarrel emerged from this week’s debate in South Carolina, when Mrs. Clinton said she would not meet with foreign leaders, including those of Iran and North Korea, without preconditions. She later criticized Mr. Obama’s response as “irresponsible and, frankly, na?ve.”

Those four words touched off the most direct confrontation yet in the fight for the Democratic nomination. And Mr. Obama worked to keep the distinction alive during a weekend trip to Iowa, turning the disagreement into an example of how he would lead the country differently.

“Our standing in the world has diminished so much because people think that the United States wants to dictate across the world instead of cooperate across the world,” Mr. Obama said Saturday. “When we start sending a signal that we are ready to engage in serious diplomacy, then we’ve got the opportunity to stand before the world and say: We’re back. America is back.”

After Mr. Obama made his remarks, the Clinton campaign circulated a column from The Miami Herald, quoting Mr. Obama only days earlier saying he would set conditions before meeting with President Hugo Chávez of Venezuela. “Under certain conditions, I always believe in talking,” Mr. Obama told the newspaper. A spokesman for the senator, Robert Gibbs, confirmed the remark, but said there was no conflict, adding, “The meeting would have to be in the national interest.”

While Mrs. Clinton did not enter the fray Saturday, her aides enlisted former Gov. Tom Vilsack of Iowa, a co-chairman of the Clinton campaign, to respond in a hastily arranged call with reporters. Mr. Vilsack defended Mrs. Clinton’s foreign policy approach and criticized Mr. Obama, saying, “I think it reflects a curious approach, a curious judgment on the part of the good senator.”