PRINCETON, N.J., May 8 (UPI) -- U.S. President George Bush's approval rating in his party has fallen, with 6-in-10 Republicans approving of the job he's doing, a Gallup poll indicates.

Throughout his presidency, Bush averaged 85 percent approval among Republicans, including 92 percent during his first term and 77 percent in his second term until the 60 percent registered in the latest survey, the Gallup poll released Thursday indicated.

Overall, Bush's job approval rating is 28 percent, the worst of his administration and tying the lowest for any president since Jimmy Carter's 28 percent approval rating in 1979, Gallup said.

Pollsters at the Princeton, N.J., company said lower support among Republicans is the main reason behind the drop in Bush's overall rating. His approval ratings among Democrats and independents were low already.

The culprit for the decline in Bush's overall job approval rating could be rising gas prices, which historically weigh down presidential approval ratings, pollsters said.

The survey interviewed 1,019 adults May 1-3. Results for the overall sample have a margin of error of 3 percentage points. Results based on the sample of 287 Republicans have a margin of error of 6 percentage points.