BAYAMON, Puerto Rico (AP) _ Barack Obama told veterans Saturday that he can't understand why Republican John McCain opposes legislation that would provide college scholarships to people who have served in the U.S. military.

"Now, let me be clear: No one can dispute John McCain's love for this country or his concern for veterans. But here's what I don't understand. I don't understand why John McCain would side with George Bush and oppose our plan to make college more affordable for our veterans," the Democratic presidential candidate said. "George Bush and John McCain may think our plan is too generous. I could not disagree more."

Obama's criticism renews a clash that turned personal after the Senate approved the scholarship bill Thursday.

During the Senate debate, the Illinois senator questioned why McCain a Navy veteran and former prisoner of war would oppose the measure.

McCain responded with a sharp statement saying that he wouldn't listen to any lectures on veterans' affairs from Obama, "who did not feel it was his responsibility to serve our country in uniform."

Obama, speaking to reporters aboard his plane Saturday, countered that the idea that he can't speak on veterans' issues because he didn't serve in the military "makes no sense whatsoever."

"I didn't serve, as many people my age, because the Vietnam war was over by the time I was of draft age and we went to an all-volunteer Army. But obviously I revere our soldiers and want to make sure they are being treated with honor and respect," he added.

The Arizona senator opposes the scholarship measure, as does the Pentagon, because it applies to people who serve just three years. He fears that would encourage people to leave the military after only one enlistment even as the U.S. fights two wars and is trying to increase the size of the Army and Marine Corps.

Instead, McCain and Republican colleagues proposed a bill to increase benefits in conjunction with a veteran's length of service. Senate Democrats blocked that measure.

"While Barack Obama engages in the same tired partisan politics that has failed our veterans time and again, John McCain has offered legislation that will expand needed education benefits for veterans while promoting retention in our armed forces," McCain spokesman Brian Rogers said Saturday.

Only three primaries are left in the battle for the Democratic nomination, and Puerto Rico is holding one of them. Puerto Ricans can vote in party primaries but not in the fall general election.

Hillary Rodham Clinton spoke at an evening rally in Aguadilla, where she reminded the crowd of her ties to Puerto Rico as a first lady and then as senator from New York, which has approximately 1 million Puerto Rican residents.

"My commitment to Puerto Rico did not start last month or last year," she said. "I will always be your voice as president."

Through her speech, Clinton drew applause by insisting Puerto Ricans should get the same tax breaks, health care and economic opportunity afforded mainland U.S. citizens.

"You deserve a president who will give Puerto Rico's issues as much attention as the president gives to any state," she said.