After hitting a high point of 57 percent late last week, support for McCain slipped to 52 percent, The Gallup Poll Daily tracking report for Sunday-Tuesday said.
Huckabee moved up to 28 percent from 23 percent.
The Gallup Poll Daily tracking also found that nearly half of Republicans and Republican-leaning voters nationwide said they supported Huckabee, Rep. Ron Paul of Texas, political activist Alan Keyes, "Other," or have no opinion, the Princeton, N.J., firm said.
The tracking poll indicated virtually no change in the Democratic race since Friday-through-Sunday polling. Sen. Hillary Clinton of New York and Barack Obama of Illinois remained in a statistical tie, with Clinton at 45 percent and Obama at 44 percent.
Results are based on combined data from Saturday through Tuesday, including interviews with 963 Republican and Republican-leaning voters, and 1,262 Democratic and Democratic-leaning voters, Gallup said. The margin of error is plus or minus 3 percentage points.