By David DeKok
HARRISBURG, Pa., Oct 29 (Reuters) - Pennsylvania Governor Tom Corbett is closing in but still trails his Democratic challenger among likely voters in next week's gubernatorial election, a poll showed on Wednesday.
Democrat Tom Wolf leads 53 to 40 percent over the Republican incumbent, according to the Franklin & Marshall College poll.
The latest results show the gap is narrowing. A Quinnipiac University poll had Wolf with a 17-point lead in early October.
A loss at the ballot box on Nov. 4 would make Corbett the state's first incumbent governor to lose a re-election bid.
Corbett's gain in the poll could be due to his campaign television ads that say Wolf wants to raise taxes on the middle class, said Terry Madonna, director of the Franklin & Marshall poll.
But no incumbent governor in Pennsylvania has ever trailed by double digits this close to an election, Madonna said.
"It would be a comeback of gigantic proportions," he said.
Going after Wolf as a tax-and-spend liberal, Republicans criticize the Democratic businessman as not being forthcoming about his tax reform plans.
Wolf supports fairer taxes and no tax increase on the middle class but says many of the specifics would depend on the state's fiscal health.
Former President Bill Clinton campaigned for Wolf on Tuesday in Pittsburgh, and President Obama was expected to help out in Philadelphia on Sunday.
Among Republicans, Governor Chris Christie of New Jersey and Governor Rick Perry of Texas have campaigned for Corbett.
The Franklin & Marshall telephone poll of 738 registered voters, conducted October 20 to October 26, had a margin of error of plus or minus 3.5 percentage points. (Editing by Barbara Goldberg, Ellen Wulfhorst and Richard Chang)