While some polls show that Sen. John McCain (R-Ariz.) is running even with Sen. Barack Obama (D-Ill.) in general election matchups, the Republican has to be considered the underdog — and will need a compelling positive vision for America to catch up.

[IMGCAP(1)]McCain needs to advance a reformist-conservative alternative to Obama’s “Yes, We Can” appeal — perhaps updating his 2000 Theodore Roosevelt image — and focus on the economy and health care as well as national security.

McCain said this week that if the Iraq War goes badly between now and November, “I lose,” but it’s not necessarily true that if Iraq goes well, he wins.

He ought to. On what used to be the most important issue in America, McCain was one of a bare handful of politicians, including Republicans, who believed America had to win the war and could.

If, this fall, the evidence shows he was correct, his Democratic opponent — presumably Obama, but Sen. Hillary Rodham Clinton (N.Y.), too — ought to be discredited as a potential commander in chief for advocating withdrawal and losing the war, as they do even now.

Sadly, though, politics doesn’t work that way. History is strewn with leaders cast aside after a war because their countrymen wanted to “move on.” The list includes Winston Churchill and George H.W. Bush — and this war is not likely to be as decisively won as theirs were.

The country already has “moved on,” making the economy Issue One, followed by health care, energy, education and immigration.

McCain is going to have to play both offense and defense on the economy — proving that he does not represent, as Obama charges, “George Bush’s third term,” and that Obama’s tax increases will be disastrous for the economy and that his own economic vision will produce growth, opportunity and higher incomes for workers.

Right now, Americans don’t believe in Republican economics, and McCain is especially vulnerable because he has flip-flopped on Bush’s tax cuts, once declaring them gifts to the rich and now saying he wants to extend them.

McCain is going to have to teach economics to a doubting country — and, first, he is going to have to learn some himself. He also might want to select a running mate who is an expert on the subject, say former Rep. Rob Portman (R-Ohio) or even his detested former rival, Mitt Romney.

He is going to have to say more, when asked about the economy, than “we’ve got to cut spending,” which he’s been doing incessantly during primary debates. Americans plainly want the government to spend — that is, invest — in health care, education, infrastructure, science and alternative energy sources.

In his post-Wisconsin victory speech Feb. 19, delivered in Columbus, Ohio, McCain did lay out the beginnings of an agenda, promising to “save Social Security and Medicare without the tricks, lies and posturing that have failed us for too long” and “make the tax code simpler, flatter, fairer, more pro-growth and pro-jobs.”

He also set as goals to reduce “our dangerous dependence on foreign oil with an energy policy that encourages American industry and technology,” to “help Americans without health insurance acquire it without bankrupting the country” and “make our public schools more accountable to parents and better able to prepare our children for the challenges they’ll meet in the world.”

It was a good beginning, but it was only that. On health care, for instance, Obama and Clinton have full-blown plans for insuring all (or nearly all) Americans. McCain’s proposed $2,500 refundable tax credit would not buy much insurance for the uninsured.

Former Sen. Bill Frist (R-Tenn.), now teaching health economics at Princeton, says Obama’s and Clinton’s health care plans will cost not $110 billion a year, as they say, but three times that. McCain needs to talk to Frist and adopt the argument, if he can prove it.

In his Feb. 19 speech, McCain declared: “I’m not the youngest candidate, but I am the most experienced. … I know how Congress works, and how to make it work for the country and not just the re-election of its Members. I know how the world works. I know the good and evil in it.”

He does have vastly more experience than Obama, but the experience argument was tried by Clinton and did not work. Arguably, it might work better in the general election, but that has to be balanced against McCain’s age, health and the fact that he’s “so Washington,” and a friend of lobbyists, at that.

McCain has to remind people that for most of his career, he’s been exactly the “change agent” that Obama promises to be. And he has to lay out an agenda of change.

He also needs to get Congressional Republicans to be part of his “change agenda” — both to unify the party and to see to it that he’s not dragged down by their negatives.

McCain hopes to show that Obama represents nothing but “an eloquent but empty call for change” and a return to liberal big government. He has every right to do so. Obama is short on accomplishments, especially of the bipartisan variety.

But McCain needs more. On Feb. 19, he promised that “we will make the right changes to restore the people’s trust in their government and meet the great challenges of our time with wisdom and with faith in the values and ability of Americans for whom no challenge is greater than their resolve, courage and patriotism.”

The words read like Ronald Reagan, but it was ponderous when McCain read them — seemingly for the first time. To beat Obama, McCain also has to practice speechmaking.