SEATTLE — In a rare face-off on foreign policy, President Barack Obama and Republican rival Mitt Romney are swapping sharp criticism but exposing few clear policy differences on key national security matters.

For Romney, who seeks to boost his foreign policy credentials as he begins a high-stakes trip abroad, a lack of specific proposals has exposed him to a flurry of criticism from Obama and his surrogates. Just over three months from Election Day, the president's team has dug in on its efforts to cast the Republican as a national security lightweight while trying to capitalize on Obama's strength on such issues.

Following Romney's speech Tuesday to the Veterans of Foreign Wars convention, Vice President Joe Biden said Romney "reflexively criticizes the president's policies without offering any alternatives."