(CNN) -- Sen. John McCain stepped up his rhetoric against his Democratic rival on taxes in his weekly radio address Saturday, comparing his plan to "socialist" programs.

The remarks were part of a theme McCain has used since the final presidential debate, but his most recent comments were the first time he used the word to describe Sen. Barack Obama.

In the radio address, McCain didn't directly call Obama a socialist, but he let the now-famous Joe "the Plumber" Wurzelbacher nearly do it for him.

"You see, [Obama] believes in redistributing wealth, not in policies that help us all make more of it. Joe, in his plainspoken way, said this sounded a lot like socialism," McCain said Saturday. Watch McCain blast Obama »

In an interview with ABC last week, Wurzelbacher said Obama's proposal to raise taxes by 3 percent on those making $250,000 and over is a "very socialist view."

Republican vice presidential candidate Sarah Palin has used the word in speeches the past two days as well. Watch more on the state of the presidential race »

McCain also said in his radio address, "At least in Europe, the socialist leaders who so admire my opponent are up front about their objectives. They use real numbers and honest language. And we should demand equal candor from Sen. Obama. Raising taxes on some in order to give checks to others is not a tax cut; it's just another government giveaway."

On the campaign trail Saturday in Concord, North Carolina, he added that Americans have seen sharing the wealth in other countries before. But he quoted Obama as saying he wants to "spread the wealth around." Fact Check: Did Obama say he would "spread the wealth around"?

"Spread the wealth around. We have seen that movie before in other countries and attempts by the liberal left before," McCain said.

In his speech, McCain also said, "This explains some big problems with my opponent's claim that he will cut income taxes for 95 percent of Americans. You might ask, how do you cut income taxes for 90 percent of Americans when more than 40 percent pay no income taxes right now?

"How do you reduce the number zero? That's the key to Barack Obama's whole plan: Since you can't reduce taxes on those who pay zero, the government will write them all checks called a tax credit. And the Treasury will have to cover those checks by taxing other people. ... The Obama tax increase would come at the worst possible time for America."

Asked why McCain used the word "socialist" in the radio remarks, a spokesman said, "That's what it is. 'Spreading the wealth' around is socialism."

In a July interview with the Kansas City Star, McCain said Obama had the "most extreme" record in the Senate. He said in a comment he has since repeated on the trail, "his voting record ... is more to the left than the announced socialist in the United States Senate, Bernie Sanders of Vermont."

Pressed on whether he considered Obama a socialist, McCain shrugged and said, "I don't know."

Obama hit back against the McCain campaign's accusations Saturday in Missouri and said the Republican nominee was ignoring the needs of America's middle class.

"John McCain is so out of touch with the struggles you are facing that he must be the first politician in history to call a tax cut for working people 'welfare,' " Obama told a massive crowd under the famous St. Louis arch. "The only 'welfare' in this campaign is John McCain's plan to give another $200 billion in tax cuts to the wealthiest corporations in America." Watch large crowds rally for Obama »

"George Bush and John McCain are out of ideas, they are out of touch, and if you stand with me, in 17 days they'll be out of time," Obama added to wild applause.

The Obama campaign said police in St. Louis estimated the crowd size at 100,000 people. Watch large crowds rally for Obama »

In remarks this week, Palin referred to Obama's encounter with "Joe the Plumber" in Ohio on Sunday.

At a rally Friday in West Chester, Ohio, where one banner in the crowd read, "Obama is a Socialist/Marxist," Palin said, "Joe suggested that that sounded a little bit like socialism. Whatever you call it, I call it bad medicine for an ailing economy, and it's what Barack Obama will do to those who want to create jobs, and we're willing to call Barack Obama on it."

Palin invoked Wurzelbacher again Saturday, needling Obama for having a "staged photo-op" interrupted by a voter asking him a question about taxes.

"So when he left Joe's neighborhood in Toledo, our opponent didn't look real happy," Palin, speaking in Pennsylvania, said of Obama. "Seems that the staged photo-op there got ruined by a real person's question."

"So here's a guy working -- standing there in his neighborhood when a candidate for president shows up, and he wanted more than just a handshake and a campaign button. He wanted some answers."

A similar thing happened to Palin on September 27 in Philadelphia at one of her own photo-ops. Temple graduate student Michael Rovito approached the governor at a cheesesteak shop to ask her opinions on cross-border raids into Pakistan to hunt terrorists.

Palin told Rovito that the United States should "absolutely" attack within Pakistan to stop terrorists, a position at odds with McCain's.

The remark was picked up by a network camera crew and caused a headache for the GOP ticket. Staffers were forced to explain the two candidates' apparently conflicting views on national television days later.

Palin arrived in New York on Saturday afternoon and headed to NBC headquarters at Rockefeller Center for rehearsals before making her much-anticipated debut on "Saturday Night Live."

CNN's Steve Brusk, Tasha Diakides, Peter Hamby, Ed Hornick, Sasha Johnson and Alexander Marquardt contributed to this report.

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