WASHINGTON (AP) _ Republican John McCain and Democratic U.S. presidential rival Barack Obama were trading barbs as they began crisscrossing three Western states that are likely to be pivotal battlegrounds that could decide the November presidential election.

The two candidates recently have largely ignored Hillary Rodham Clinton, Obama's long-shot rival, who campaigned Monday in Puerto Rico. The U.S. Caribbean territory's primary on June 1 is one of just three left as the intense months-long battle for the Democratic presidential nomination winds down and Obama looks to be the inevitable nominee.

Obama was signaling, even before the Democratic primary campaign formally wraps up, that he intends to fight this fall for three Western states — New Mexico, Nevada and Colorado — that narrowly went Republican four years ago.

"We're going to fight as hard as we can in these states. We want to send the message now that we're going to go after them and I expect to win them," the Illinois senator said Monday in New Mexico.

McCain also spent the Memorial Day holiday in New Mexico where he used the occasion to criticize Obama for not having been to Iraq since 2006 and portray the first-term Democratic senator as naive on foreign policy and not experienced enough to lead the military.

Obama acknowledged that unlike McCain he has no military experience, but said he is committed to strengthening the military and improving veterans' services.

"As president of the United States, I will not let you down," he promised a group of veterans in New Mexico, a battleground state in the general election.

On Tuesday, Obama was heading to Nevada for campaign events in the Las Vegas area, where he was expected to focus on economic issues. In April, Nevada posted the worst foreclosure rate in the U.S., with one in every 146 households receiving a foreclosure-related notice, nearly four times the national rate.

Obama said he needs to introduce himself to Western voters. Issues like improving the economy, ending the Iraq war and providing universal health care will appeal to everyone, he said.

"I'm absolutely confident that we're going to do very well ... here because people out west are independent-minded and are going to look at whether or not over the last eight years the country is better off under Republican rule. I think they're going to conclude they're not and they want fundamental change, something that I'm offering and John McCain is not," he said.

McCain said Obama "has no experience, no knowledge or background" on Western issues.

"I believe as a Western senator I understand the issues, the challenges of the future for these ... states, whether it be land, water, Native American issues, preservation, environmental issues," McCain said in an interview with The Associated Press.

McCain was scheduled to speak in Denver on Tuesday before heading the following day for a town hall meeting in Reno, Nevada. Obama was heading to Colorado later in the week.

Together, the three states account for only 19 of the 270 electoral votes needed to win the White House. But those votes could be vital in a close race, particularly if Obama's weakness among white, working-class voters carries over from the primary race with Clinton and cuts his chance of winning some other states where Democrats usually do well.

U.S. President George W. Bush won New Mexico over John Kerry four years ago by the tiniest of margins — 49.84 percent to 49.05. His margins were not a whole lot bigger in Nevada (50.5 to 47.9) and Colorado (51.7 to 47).