With Republicans moving ever further to the right and Democrats to the left — though not so far as Republicans are to the right — there really is a crying need for a centrist alternative.

President Barack Obama hopes to win re-election with populist appeals for “fairness,” meaning raising taxes on the highest earners regardless of whether it makes economic sense.

His presumptive GOP opponent, former Massachusetts Gov. Mitt Romney, has spent the past year pandering to the tea party and now has endorsed a House Republican budget that practically eliminates federal investment in human capital.

What the nation needs is a third-party candidate who’ll advocate tax and entitlement reform and a leaner, performance-based government that invests smartly in education, research and infrastructure.

That candidate could borrow good ideas from both parties — such as the “premium support” Medicare plan proposed by Rep. Paul Ryan (R-Wis.) and Sen. Ron Wyden (D-Ore.) — but ought to campaign for real on the problem-solving, “bring us together” promise that Obama (and George W. Bush) ran on, then abandoned.

I’m hoping that someone with political credibility will step up and run for president using the 50-state ballot access that the Americans Elect organization is in the process of securing for its ticket.

Say, former Indiana Sen. (and Gov.) Evan Bayh (D), who by the Americans Elect rules would have to choose a Republican as his running mate. Say, Sen. Olympia Snowe (Maine).

I cite those two because they’re experienced and denounced the dysfunction of government as they announced their exits from public office.

Alas, so far only a passel of no-names or near-no-names has declared candidacy on the AE website — led by former Louisiana Gov. Buddy Roemer (R) and former Salt Lake City Mayor Rocky Anderson (D).

Bayh and Snowe are among 300 or so “draft” candidates who have been proposed by others, along with some other worthy possibilities including New York Mayor Michael Bloomberg, former Utah Gov. Jon Huntsman and former Comptroller General David Walker, who seems most likely to actually run.

As one of the nation’s leading advocates of fiscal sanity and government reform, Walker could be a strong candidate — if he could attract the funding to establish widespread name recognition and get his message across.

All third-party candidates in the past have failed to win, of course, but some have moved — or scared — the major parties into addressing issues they were otherwise avoiding. And that’s the great benefit that a credible AE candidate could perform in 2012.

This year, it’s not one issue that needs addressing — it’s a whole series of problems that Republicans and Democrats can’t or won’t solve because they are so ideologically divided.

The problems start with getting job creation started again, which includes investment in education, research and infrastructure (which Obama favors) and tax reform (which both candidates merely give lip service to).

They include tackling the massive federal debt, which will increase under Obama’s budget from 80 percent of gross domestic product now to a crushing 124 percent by 2050, according to the Committee for a Responsible Federal Budget.

The House Republican budget drafted by Ryan and declared “marvelous” by Romney reduces the debt to just 10 percent of GDP, according to the Congressional Budget Office. But it achieves this by slashing domestic discretionary programs — everything from the FBI and Border Patrol to education and national parks — to less than 1 percent of GDP from the present 4 percent, according to figures from the Committee for a Responsible Federal Budget.

A centrist energy policy would be a true “do it all” approach — drilling now, researching alternatives and gradually raising carbon taxes.

Neither Obama nor Romney has even addressed the most immediate threat to the American economy — the “fiscal cliff” we’re approaching at the end of this year thanks to the two parties’ repeated refusal to make policy choices in a timely manner.

At the end of the year, the Bush tax cuts expire. So do “patches” protecting middle-class taxpayers from paying the alternative minimum tax, the 2 percent payroll tax holiday and expanded unemployment benefits.

Doctors will see reimbursements for Medicare patients cut by 22 percent, or $40 billion. And the automatic spending sequester imposed when the Congressional super committee failed to agree on budget cuts last summer will reduce defense outlays by 10 percent and non-defense spending by 8 percent for a total one-year drop of $160 billion.

According to the Committee for a Responsible Federal Budget, those hits “would be roughly equivalent to taking 3.5 percent of GDP out of the economy.” The Congressional Budget Office estimates that the unemployment rate will rise by 1.1 percent next year.

On top of all this, the current extension of the federal debt ceiling expires at the end of the year. Failure to raise it would lead to the default narrowly avoided last year.

My guess, my hope, would be that a centrist candidate would propose Simpson-Bowles as the answer to most of the issues involved with deficits and debt — the 4-to-1 spending-cut/revenue-increase formula recommended by Obama’s debt commission in 2011 and promptly abandoned by the president.

While Obama appeals to a base of liberals (20 percent of the electorate) and Democrats (31 percent) and Romney appeals to Republicans (27 percent) and conservatives (40 percent), a third-party candidate could draw from independents (40 percent) and moderates (35 percent).

It would be a worthy fight to wage.