American moderates are abandoning the Democratic and Republican parties in large numbers, and calling themselves politically independent.

That's the finding of a new poll from the Pew Research Center. Just 32 percent of the people surveyed say they are Democrats, and 24 percent now call themselves Republicans. And 38 percent reject both parties and call themselves independents.

The vast majority of Republicans say they are conservative -- while conservative Democrats have become scarce. And those who do align themselves with a party are more ideological and more polarized than at any point in the past 25 years.

The sharpest differences between partisans are mostly on the issues at the core of this year's campaign -- regarding the role of government, and whether regulation hurts or helps business. There are sharp differences on the question of how much of a "social safety net" the government should provide.

President Barack Obama holds a slim edge over Mitt Romney in the poll, 49 percent to 45 percent among registered voters. The results suggest that the sharpest divides between their supporters are over the role and effectiveness of government.