ASPEN, Colo. — Michael Bloomberg should have been here. At the annual Aspen Institute Ideas Festival last week, he could have won influential recruits for his possible independent presidential campaign, basked in glowing approval of initiatives he’s taken as New York mayor and helped develop a wider political agenda. [IMGCAP(1)]

The festival is attended mainly by rich social liberals of a distinctly entrepreneurial bent who this year adored former President Bill Clinton and disbelieved White House aide Karl Rove as they delivered equally data-laden tours of the policy horizon.

I took no poll, but I’d bet this crowd would love Bloomberg — for his social views, his record of achievement in New York and his denunciations of the dismal mire that partisan politics has created in Washington, D.C.

Another piece of evidence is that the hands-down hero of last year’s festival was Joel Klein, the former Clinton White House aide who now is Bloomberg’s revolution-making schools chancellor and who said he’d support Bloomberg if he ran for president.

If he does run, Bloomberg doesn’t need the money these CEOs and philanthropists could contribute. He can afford to self-finance his campaign. But he could use their endorsements to gain credibility.

It would help, too, if they got behind the Unity08 third-party effort that seems to represent Bloomberg’s best avenue to get on the ballot in all 50 states.

According to one of its founders, Gerald Rafshoon, Unity08 currently has 100,000 party members, hopes to have 1 million by late fall and hopes to have 10 million participate in its Internet nominating convention next June.

“If I were Michael Bloomberg,” Rafshoon told me, “I think it would be best to be validated by a constituency of 10 million people rather than just spending his own money.” Rafshoon emphasized that he hoped other candidates would compete, but it’s clear that Bloomberg represents the best third-party shot on the horizon.

Of course, it’s a long shot — partly because no third-party candidate has ever won the presidency and partly because Bloomberg so far doesn’t represent the kind of vivid alternative that Teddy Roosevelt did in 1912 or that even Ross Perot did in 1992.

Bloomberg is easily caricatured — even by himself — as a short, divorced, Jewish New Yorker, pro-choice, pro-gay rights, anti-gun and anti-smoking. It’s not exactly the kind of populist profile that will light prairie fires across America.

But Bloomberg does have this going for him — a heavy swatch of the country is totally fed up with zero-sum partisan warfare. And he has a sterling record as an innovative problem-solver at a time when America has a lot of problems that people want solved.

A Bloomberg candidacy wouldn’t be necessary if Democrats and/or Republicans nominate a nonpolarizing problem-solver with a hope of reuniting the country, not further dividing it.

Let’s hope that happens. But, just in case, Bloomberg should be developing a compelling agenda that can trump his identity problems.

It needs to include a new national security policy that offers a choice between Republicans’ overreliance on military force and Democrats’ overreliance on polite diplomacy. Bloomberg needs to say what he’d do about Iraq and Iran, Palestine and Pakistan.

He does have an energy/environment agenda, designed to cut New York’s carbon emissions by 30 percent by 2030, which Clinton praised at the ideas festival.

“All the press was about the mayor’s plan to charge for the right to drive in Manhattan,” Clinton said, “but 80 percent of emissions come from buildings and just think how many jobs you can create changing black tar roofs to green. You can’t outsource those jobs to India. Somebody’s got to be in that roof planting sod.”

The Aspen festival produced discussion of a wealth of novel proposals on health care reform, early childhood education, China policy and the global economy that Bloomberg could have absorbed for his agenda.

And he could have given something back — encouragement to frustrated high-rollers that there might be an alternative to Washington’s incessant partisan warfare.

At another gathering this summer, the “Ceasefire! Bridging the Political Divide” conference in Los Angeles last month, Bloomberg declared that “the politics of partisanship and the resulting inaction and excuses have paralyzed decision-making, especially at the federal level.

“The big issues of the day are not being addressed — leaving our future in jeopardy. We can accept this, or we can say ‘enough is enough’ — and together build a bright future for our country,” he said.

Bloomberg’s best line in a speech that could have used some cliché-deletion was that “Washington is sinking into a swamp of dysfunction. No matter who is in charge today, sadly, partisanship is king.” That would have gone over big in Aspen.

Of course, it also has to go over big in Albuquerque and Augusta, Peoria and Plainsville. Delivered by a New Yorker, it has to be backed up by proposals that will appeal to average Americans — honest ones, as Bloomberg says, that reveal the downsides as well as the upsides.

Bloomberg might never run, or he might run and lose. But if he just fashions an alternative agenda and gives voice to “post-partisanship,” he’ll be doing the country a favor.