* Obama says 19 days from beginning, not end
* Polls show Obama with edge over McCain
* McCain works Joe the plumber into his stump speech
By John Whitesides, Political Correspondent
NEW YORK, Oct 16 (Reuters) - Democratic presidential nominee Barack Obama warned his supporters to guard against overconfidence on Thursday as he and underdog Republican rival John McCain opened a 19-day sprint to Election Day.
The two candidates hit the campaign trail — Obama in New York and New Hampshire and McCain in Pennsylvania — after their third and last presidential debate on Wednesday, a testy face-off that made an Ohio plumber famous.
So far, all the stars seemed to be lining up in Obama’s favor. He leads in national opinion polls and in many of the battleground states where the Nov. 4 race will be won or lost.
Late on Thursday, The Washington Post delivered an endorsement of Obama and a rebuke to McCain in an editorial on its web site (www.washingtonpost.com). The Post, one of America’s most respected newspapers, said its endorsement of Obama was “without ambivalence.”
“The choice is made easy in part by Mr. McCain’s disappointing campaign, above all his irresponsible selection of a running mate who is not ready to be president,” the Post editors wrote. “It is made easy in larger part, though, because of our admiration for Mr. Obama and the impressive qualities he has shown during this long race.”
A confident but cautious Obama told supporters in New York, “We are now 19 days not from the end but from the beginning. The amount of work that’s going to be involved for the next president will be extraordinary.”
Traders betting on future events in the political prediction markets are overwhelmingly predicting an Obama victory, giving the Illinois Democrat a better than 80 percent chance of winning.
Ireland’s biggest bookmaker, Paddy Power, was already declaring Obama the winner. The Dublin-based bookmaker said it would pay out early more than 1 million euros ($1.35 million) on bets that Obama will be the next U.S. president.
But Obama pointed out to deep-pocket contributors at a fundraising breakfast in Manhattan, and later to supporters in a driving rain in Londonderry, New Hampshire, that he was supposed to win New Hampshire last January in the Democratic primary but lost the state to Sen. Hillary Clinton.
“We are 19 days away from changing this country — 19 days. But for those who are getting a little cocky, I’ve got two words for you: New Hampshire. I learned right here that you can’t let up or pay too much attention to the polls,” he said.
In New York, he said, “I’ve been in these positions before when we were favored and the press starts getting carried away and we end up getting spanked.”
The new star in U.S. politics — at least for a news cycle or two — is Joe Wurzelbacher, “Joe the plumber,” who told Obama at a campaign stop that he wanted to buy a small plumbing business in Holland, Ohio.
Joe came up about two dozen times during the debate as each candidate argued that their prescriptions for America’s economic ills would help the plumber best.
Wurzelbacher was all over morning television shows and was not saying who he would vote for, but he sounded like a McCain backer.
“McCain came across with some solid points, and I was real happy about that,” he told the Toledo Blade newspaper.
McCain, speaking at a rally in Downingtown, Pennsylvania, quickly worked Wurzelbacher into his stump speech, arguing that small business operators like Joe the plumber would see their taxes go up under Obama.
“Senator Obama told Joe that he wanted to spread his wealth around. America didn’t become the greatest nation on earth by spreading the wealth; we became the greatest nation by creating new wealth,” McCain said.
“This is the choice that we face. Three weeks from now, you will choose a new president. Choose well. There is much at stake,” he said.
Although McCain went after Obama aggressively in the final debate, it might not have done much to change the shape of the race in its final stages.
Karl Rove, the architect of President George W. Bush’s two electoral victories and now a political pundit, wrote in The Wall Street Journal on Thursday that McCain faced difficult but not impossible odds.
“If Mr. McCain succeeds, he will have engineered the most impressive and improbable political comeback since Harry Truman in 1948. But having to reach back more than a half-century for inspiration is not the place campaign managers want to be now,” Rove wrote.
The two candidates were on the same stage again on Thursday night, trading wisecracks instead of campaign attacks at the Al Smith charity dinner, a political tradition in Manhattan named for the former New York governor and a regular stop for presidential candidates. (Additional reporting by Andy Sullivan and Jeff Mason; writing by Steve Holland; Editing by David Wiessler and Peter Cooney)