In 2008, those who identified themselves as conservative or moderate each amounted to 37 percent with 22 percent saying they were liberals (which was the high point for liberals dating back to 1992 in Gallup's polling). Moderates had been the biggest group for a long stretch between 1992 and 2002.

Gallup says the main reason for this trend has been the movement of independents to the conservative side. Last year, 29 percent of independents described themselves as conservative, a number that rose to 35 percent this year.

Gallup polls this year and last year say some of the issues that may be driving the trend are perceptions that there is too much regulation of government and industry, coolness to the influence of organized labor, concern over immigration, a desire to see government promote "traditional values," an increase among those who consider themselves "pro-life" on abortion and increased skepticism that there is solid evidence of global warming.

"The question is whether increased conservatism, particularly among independents, will translate into heightened support for Republican candidates," Gallup said. "Right now, it appears it may. Although Gallup polling continues to show the Democratic Party leading the Republican Party in Americans' party identification, that lead has been narrowing since the beginning of the year and now stands at six points, the smallest since 2005."