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Washington (CNN) - President Barack Obama's approval rating, a crucial indicator of his reelection chances, is on the rise, according to a new national survey.

A CNN/ORC International Poll out Tuesday also indicates that the partisan battle over extending the payroll tax may be partially responsible for the jump in the president's numbers.

According to the survey, 49% of Americans approve of the job Obama's doing in the White House, up five points from last month, with 48% saying they disapprove, down six points from mid-November. The 49% approval rating is the president's highest since May, when his number hit 54% thanks to a bounce following the killing of Osama bin Laden. Since then, in CNN polling, Obama's approval rating has hovered in the mid-40s.

"President Barack Obama's approval rating appears to be fueled by dramatic gains among middle-income Americans," says CNN Polling Director Keating Holland. "The data suggest that the debate over the payroll tax is helping Obama's efforts to portray himself as the defender of the middle class."

Obama's gains have come at the expense of the Republicans in Congress and the GOP in general. By a 50% to 31% margin, people questioned say they have more confidence in the president than in congressional Republicans to handle the major issues facing the country. Obama held a much narrower 44% to 39% margin in March.

And the GOP's overall favorable rating has dropped to six points, to 43%, since June, while the Democrats' positive rating remained steady at 55%.

"The Democrats do particularly well among middle income Americans, while the Republicans win support only from the top end of the income scale," adds Holland.

Overall, only 16% say they approve of the job Congress is doing, with 83% giving lawmakers from both parties the thumbs down. The Congressional disapproval rating has topped 80% since August in CNN polling.

The survey indicates that Obama remains personally popular, with three-quarters saying they approve of him as a person.

"Overall, it's not a bad position for an incumbent to be in as the calendar turns to an election year, but there are many months to go," says Holland.

The CNN poll was conducted by ORC International from Dec. 16 to Dec. 18, with 1,015 adult Americans questioned by telephone. The survey's overall sampling error is plus or minus three percentage points.