WASHINGTON -- A Philadelphia real-estate broker who was U.S. Sen. Rick Santorum's only Republican challenger in the Pennsylvania primary is dropping out of the race.

John Featherman yesterday said he determined that it wasn't worth the money to fight the state Republican Party, which on Tuesday challenged his application to be on the ballot.

Mr. Featherman filed 2,207 signatures with the application. The secretary of state's office tossed out 185 of them, and the party filed a challenge to 1,073 more of the signatures, said Scott Migli, executive director of the state GOP. The party cited errors such as blank boxes and Democrats who signed the petitions.

"I don't have a lot of money, and I spoke to my attorney, Sam Stretton, who was willing to go with me, willing to contest it," Mr. Featherman said. "I didn't see the sense in making our side spend any more money."

Mr. Featherman is a moderate Republican who supports abortion rights, gay marriage and a flat tax.

On Friday, Mr. Santorum's campaign manager sent Mr. Featherman a letter asking if he'd like to debate. Mr. Featherman yesterday said he is baffled as to why the senator would send such a letter if the state party was going to challenge the signatures. "The only question is why Rick Santorum's people invited me to a debate," he said.

Virginia Davis, Mr. Santorum's campaign press secretary, said the senator was keeping his promise that he would debate any primary opponent on the ballot and was not aware that the state party was going to challenge the signatures.

In 2000, Mr. Featherman, as the Libertarian Party's nominee, garnered just under 48,000 votes in a race against Mr. Santorum, Democrat Ron Klink and two other candidates. In 1998, he also ran unsuccessfully for Congress in a special election.

In the Democratic Party, state Treasurer Robert P. Casey Jr. is considered the leading candidate, and in statewide polls he has consistently run ahead of Mr. Santorum.