WASHINGTON (AP)

Buoyed by a huge fund-raising advantage and a steady lead in national polls, Democrat Barack Obama began his closing argument for the presidency on Saturday with an optimistic message that his economic policies will bring better days for hard-pressed, middle-class Americans.

Republican John McCain sought to raise doubts about his rival's tax policies and readiness to be commander in chief, as he fought desperately to stem losses in traditionally Republican-leaning states on the penultimate weekend of the testy presidential race.

Both campaigns focused on western states on Saturday. Once reliable Republican territory, much of the West has seen its politics and demographics shift over the last decade as the Hispanic population, which tends to favour Democrats, has grown,

Three states considered still in play to varying degrees - Nevada, Colorado and New Mexico - could be vital if the electoral math gets tight.

With polls showing him behind Obama nationally, McCain pledged a scrappy close to the campaign.

"We're a few points down and the pundits, of course, as they have four or five times, have written us off," he told a rally of about 1,500 supporters in Albuquerque, New Mexico. "We've got them just where we want them. We like being the underdog."

Obama mocked his Republican rival for recently trying to distance himself from the unpopular President George W. Bush.

Speaking on Saturday at a baseball stadium in the toss-up state of Nevada, Obama said it is too late for McCain to say that Bush let the economy get out of whack.

"John McCain attacking George Bush for his out-of-hand economic policy is like Dick Cheney attacking George Bush for his go-it-alone foreign policy," Obama told supporters at the rally in Reno, Nevada

McCain, pivoting from his three stops in Colorado on Friday, was also pushing hard in New Mexico on Saturday. He held a rally in Albuquerque and was later heading to Mesilla, farther south.

Make up for lost ground

The Republican candidate headed to Iowa yesterday, looking to make up for some lost ground in a Midwestern state his campaign aides argue is closer than the public polling shows. His running mate, Alaska Governor, Sarah Palin, was in Iowa on Saturday.

Obama, a senator from Illinois, unveiled a two-minute TV commercial that asks, "Will our country be better off four years from now?"

"At this defining moment in our history, the question is not, 'Are you better off than you were four years ago?' Obama says in the commercial. "We all know the answer to that." Without mentioning McCain, the ad promotes Obama's economic policies while saying that Obama will work to end "mindless partisanship" and "divisiveness".

The commercial, which which was slated to start airing in key states yesterday, highlights Obama's fund-raising superiority - most campaign commercials run 30 seconds or a minute - and the Democrat was far outspending McCain on television advertising.

'Uncertain times'

The Republican National Committee, meanwhile, released a TV commercial on Saturday questioning whether Obama has the experience to be president. The commercial, featuring the image of a stormy ocean, says the nation is in "uncertain times" that could get worse, and asks whether voters want a president "who's untested at the helm".

As the collapsing economy consumes voter attention, McCain has seized a line of attack that Obama is poised to deepen the problem by raising taxes.

Seeking to energise his backers, McCain said Obama was "more interested in controlling wealth than creating it".

"He believes in redistributing wealth," McCain told supporters at his Albuquerque rally. "We've seen that movie before in other countries. That's not America."

Obama counters that he would lower taxes for most wage-earners and that McCain's tax plan favours wealthy corporations.