HARRISBURG - Philadelphia's big Democratic turnouts tend to drown out the voices of voters elsewhere in Pennsylvania when America elects presidents.

That was the gist of Gov. Corbett's argument Thursday as he detailed for the first time his support of a Republican-led charge to change the way Pennsylvania awards its electoral votes.

If he gets his chance, Corbett told a radio audience, he will sign a bill championed by top Republican legislators to do away with the winner-take-all apportioning of the state's electoral votes. Instead, most of those votes would be parceled out based on the popular-vote winner in each of the state's congressional districts.

"It will allow the people across the state to be better represented when it comes to the vote for president," the governor said on his new monthly radio show on WPHT-AM (1210) in Philadelphia. "There are huge portions of Pennsylvania that voted for the other candidate in many of the elections, and their vote really didn't count."

The state, he told WPHT host Dom Giordano, consists of five or six distinct political regions, and he suggested they have "not been represented because of the huge turnout in Philadelphia."

The governor, a Republican, insisted the proposed change was "not a Republican-Democrat issue." But he noted that Pennsylvania has given Democrats its electoral votes in every presidential election since 1988.

In 2008, for example, a strong turnout in Democrat-rich Philadelphia helped Barack Obama win 54.7 percent of the statewide popular vote to Republican nominee John McCain's 44.3 percent. That gave Obama the state's 21 electoral votes. If the proposal backed by Corbett and GOP legislators had been the law, Obama would have split those electoral votes with McCain, 11-10.

The only other states that allocate their electoral votes by congressional district are Maine and Nebraska.

If the law is changed here, Corbett said, next year's Republican nominee might be encouraged not to "write off Pennsylvania too soon."

Democrats have branded the proposal as blatantly political, saying it is little more than a badly veiled attempt to help GOP presidential chances. They also argue that such a change would hurt Pennsylvania's interests by diminishing the state's clout in deciding who occupies the White House.

Pennsylvania, which will have 20 electoral votes in 2012, has long been considered a critical swing state in presidential elections. Candidates campaign hard here, spending huge chunks of their money and time trying to win the hearts and minds of voters.

Splitting up those 20 electoral votes would relegate the state to a minor role in national politics, U.S. Rep. Chaka Fattah (D., Pa.) said Thursday when asked about Corbett's remarks.

"What he's saying is, a Republican can't win here, so they are going to chop the state into parts and win what they can," Fattah told The Inquirer. "But that flies in the face of the facts. Republicans have won the state, and so have Democrats."

Democrats also note that Republicans are pushing the proposal even as congressional districts are being redrawn as part of the once-a-decade remapping process based on census data.

Critics have long decried the remapping process in Pennsylvania as closed to public scrutiny and open to backroom deal-making and gerrymandering. Because districts are redrawn through legislation, the party that controls the legislature and Governor's Office controls the process, and this year in Harrisburg, that party is the GOP.

Some Republicans are wary of the proposal's potential side effects on close congressional races. The Wall Street Journal reported Thursday that "Republicans worry Democrats will move campaign efforts out of safe Democratic districts in urban population centers and into the more moderate suburbs . . . [putting] extra heat on GOP House candidates."

Corbett said Thursday the effort to revamp electoral-vote distribution was meant purely to make elections fairer and more representative. "It's greater parity, greater representation to the individual citizens," he said.

Also during the radio show, the governor spelled out in greater detail his support for imposing an "impact fee" - not a tax - on companies extracting natural gas from Marcellus Shale regions of the state.

He also said he considered school vouchers a top legislative priority for the fall, along with finding more funding for transportation.

"If I had to rank them," he said, school choice would be "No. 1."

A bill introduced this year would offer state-funded tuition vouchers averaging roughly $7,000 per pupil to families wanting to transfer their children from failing public schools to private or parochial schools. The bill faces stiff opposition from teachers' unions. On his radio show, Corbett noted that he and his wife, Sue, had been teachers, and said he had no problem with teachers, just with their union leaders.

Regarding the Marcellus Shale, Corbett said his administration would push legislation within the next two weeks to establish an impact fee.

He said the money it raised would not go into the general state budget, but would be used primarily to compensate communities where drilling is taking place for the damage to their roads and bridges from heavy truck traffic and other local impacts.

"The primary amount of money - a huge amount of money - will go to the counties, and let the counties work with the municipalities," Corbett said. "What comes to the state, in my mind, will be used exclusively for the [Pennsylvania Emergency Management Agency] and will be used for environmental cleanup."

Corbett has been under intensifying pressure for months - from some fellow Republicans as well as Democrats - to support a fee that would pay for environmental cleanup and compensate communities where drilling is done.

He had stuck to a pledge he made in last year's gubernatorial campaign to oppose any new taxes or fees on anyone for anything.

Since taking office in January, Corbett has softened that stance, saying at first that he would consider a local impact fee on the drillers, then saying he was in talks about one with GOP legislative leaders. His Marcellus Shale Advisory Commission studied the issue and recommended an impact fee.

Corbett did not specify the size or scope of his impact-fee proposal. But he said he had preliminary talks with legislative leaders, adding, "We will give them our package in a week or two."

Contact staff writer Angela Couloumbis at 717-787-5934, acouloumbis@phillynews.com, or @AngelasInk on Twitter.