More than four in 10 Americans see themselves as belonging to the middle class, and a new Washington Post-ABC News poll finds that if the 2012 election were held today, they would split 50 percent for President Obama vs. 46 percent for Mitt Romney.

The middle class already represents a sizable electoral force, swelling to a majority when “upper middle class” is taken into account. And although politicians proclaim how their policies will help middle-class families, the survey reveals big differences between voters who feel secure in their economic position and those who fear it’s slipping away.

Obama leads Romney by 20 percentage points among voters who are “comfortable” in the middle class and those who are “moving up” beyond it. But Romney counters with a 23-point edge among those who say they are “struggling” to hang on. Both are more lopsided than voters at the highest and lowest end of the economic spectrum. Voters who call themselves “upper middle class” and even better off split 47 percent for Obama, 51 percent for Romney, and the candidates are also close among voters who say they are working class or below.

Struggling middle-class dwellers are deeply negative on Obama’s economic record. More than three-quarters disapprove of Obama’s handling of the economy, and 53 percent say it’s a major reason to oppose him this fall. By contrast, four in 10 of those who are comfortable in the middle class disapprove of Obama on the economy.

Looking forward, those who are comfortable or moving up beyond the middle class trust Obama over Romney to protect the middle class by a 57 to 33 percent margin. “Struggling” middle-class Americans tilt toward Romney, but by a less lopsided 48 to 40 percent.

Breaking the trend, the divergent middle-class constituencies align on the question of fairness and overregulation. About half of both groups see “unfairness in the economic system that favors the wealthy” as a bigger problem than “overregulation of the free market that interferes with growth and prosperity.”

People who see themselves as middle class don’t fit squarely into income and educational boxes. In the Post-ABC poll, more than four in 10 report annual incomes under $50,000, but 17 percent make $100,000 or more. Like most Americans, most of the middle class lacks a four-year college degree, and more than a third has no education past high school.

By contrast, socioeconomic lines clearly define the working and upper middle classes. For instance, more than three-quarters of those who see themselves as working class or worse off report incomes under $50,000, while more than six in 10 upper-middle-class or higher voters make $100,000 or more.

Read full poll results

More from the Post polling team

Sign up for Post polling e-mails

Follow Post polling on Twitter

Like Post Politics on Facebook