HARRISBURG - The state Republican Party is challenging candidate petitions by members of the Constitution and Libertarian Parties, seeking to bounce from the state ballot candidates for president, vice president, and several other offices.

Line-by-line reviews of the candidates' petition signatures ordered by a state Commonwealth Court judge will begin Monday at the Philadelphia Board of Elections.

Analysts say Republicans are probably worried that conservatives dissatisfied with their presidential candidate, Mitt Romney, will defect to Constitution or Libertarian candidates.

The issues that tend to attract those two party's activists, such as limited government, tend to also be key for many Republicans, said Terry Madonna, a professor of public affairs and director of the Center for Opinion Research at Franklin and Marshall College.

In the most recent public poll, released Thursday by Franklin and Marshall, President Obama is ahead of Romney, 44 percent to 38 percent, with 15 percent undecided. The poll's margin of error is plus or minus 3.8 percentage points.

A Republican Party spokeswoman said the GOP was challenging the nominating papers because they are riddled with errors, and the party is concerned that Democrats are behind the petitions.

The petitions, spokeswoman Valerie Caras said, were circulated by and signed largely by Democrats.

The president of the Libertarian Party of Pennsylvania, Tom Stevens, said the petition drive was financed strictly by Libertarian Party members and the campaign of former New Mexico Gov. Gary Johnson, the party's candidate for president.

"It's part of no plot, and no money is coming from Democrats to finance our petition drive," Stevens said.

He said it may be true that the signers and circulators were Democrats. But they were hired exclusively by a contractor for the national Libertarian Party, and they must accurately represent the Libertarian Party and its philosophies, he said.

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Pa. GOP targets 2 parties' petitions