RENO, Nev. - Battling to win the West, Republican John McCain and Democrat Barack Obama are tripping over each other this week in New Mexico, Nevada and Colorado.

President Bush narrowly won them four years ago; Democrats now see them as ripe for the taking.

"I'm a Western senator," McCain, the GOP nominee-in-waiting from Arizona, said in this gambling town yesterday, signaling he intends to fiercely defend the turf. "I understand our issues."

Obama, who has nearly secured the Democratic nomination for president, sounds just as determined.

"We can win the West," the Illinois senator said Monday at a museum in Las Cruces, N.M., as he stood alongside the state's Democratic governor, Bill Richardson, a prominent Hispanic.

Once a GOP stronghold, the West has changed demographically - and thus politically - over the last decade.

Retirees from all over, many from the liberal Northeast and West Coast, flocked to the region because of its relatively cheap land, its dry, warm climate, its range of recreational opportunities, and its magnificent mountains and sprawling deserts.

Businesses sprouted in the region's few dense population centers, and job opportunities followed. So did swing-voting Hispanic immigrants.

That growth has exploded since the last presidential election. Census figures show that between July 2004 and July 2007, Nevada grew 10.1 percent, Colorado 5.5 percent, and New Mexico 4.1 percent.

Politically, the region has become far more competitive.

In 2004, Bush won New Mexico by 1 percentage point, Nevada by 2, and Colorado by 5. Of the 270 electoral votes needed for victory, the states offer a combined 19 - the number by which Democrat John Kerry fell short four years ago.

So, if Obama can win all the states that Kerry did, plus the three Western states, Democrats would win the White House after eight years of Republican rule.

Democrats argue that they now have more of a chance to take the West, and Nevada, Colorado and New Mexico are among their top targets. Arizona would have been, too, if McCain, the state's four-term senator, weren't the GOP opponent.

They note that both Colorado and New Mexico have Democratic governors.

Obama spoke to veterans on Memorial Day in Las Cruces; discussed the housing crisis in the sprawl of North Las Vegas, Nev., a day later, and talked education yesterday in Thornton, Colo.

"Understand that my starting principle is, everybody should be bilingual or everybody should be trilingual" so the United States can remain competitive, Obama said to cheers at a high school.

His allies play down concerns among some Democrats about his standing with Hispanic voters.

During the Colorado primary, Hispanics preferred Hillary Rodham Clinton to Obama by nearly 2-1, according to exit polls.

McCain's support for an eventual path to citizenship for illegal immigrants is a wild card with Hispanics.

"We have to secure our borders first," McCain said at a town-hall-style event at a local Boys & Girls Club yesterday. It is a position shift he made after broad-based legislation failed last year.