PHILADELPHIA -- A large percentage of the signatures on Ralph Nader's nomination papers to earn a place on Pennsylvania's presidential ballot appear to be invalid, his attorney told a court yesterday in a concession that casts doubt on whether he can remain there.

Lawyers for eight people sympathetic to the Democratic presidential candidate, Massachusetts Sen. John Kerry, claimed in a lawsuit that more than 37,000 of the 47,000 signatures that Nader supporters submitted in early August were either forged or flawed.

Volunteers for the Nader campaign have been reviewing the challenged signatures, and attorney Samuel Stretton told a three-judge Commonwealth Court panel yesterday that the results have not been promising.

Of the 1,371 signatures examined so far, nearly 75 percent have problems that could result in their elimination, Stretton said. More than half contained an invalid signature, 4 percent were by people not registered to vote during a required time period, and 17 percent were registered at an address different from the one listed on the petition.

A separate statistical analysis of 300 randomly selected signatures yielded similar results, Stretton said.

If that trend persists, Nader will fall short of the 25,697 valid signatures needed to keep his place on the state's ballot.

Stretton said he remained hopeful that the ratio will veer more in Nader's favor as the examination continues, but also argued that it was "humanly impossible" for the campaign to complete a full review by the state's deadline for printing its ballots.

Lawyers for the Democrats reviewed all the signatures on an equally short deadline, but Stretton said that effort had the help of a huge force of volunteers and lawyers that a third-party candidate could not hope to muster.

He said Constitutional protections require that Nader be allowed to remain on the ballot if there is not enough time for him to prepare an adequate defense to the challenge to his nomination. But that argument did not appear to impress Commonwealth Court President Judge James Gardner Colins.

"We cannot have two sets of laws, one where there are large law firms and large presidential candidates, and another where there are small law firms and third-party candidates," he said.

The lead attorney for the plaintiffs, Gregory Harvey, said that if Nader were a serious candidate for president, he would have found the volunteers needed to gather the signatures, and then defend any challenges to them.

"They have no support. They have no supporters," he said.

The dispute over the signatures may not matter. Harvey's legal team also challenged Nader's right to appear on the ballot because of a Pennsylvania law prohibiting a person who is affiliated with a political party from running as an independent.

Nader is seeking to be the Reform Party's candidate in Michigan. His running mate, Peter Camejo, is registered as a member of the Green Party. Those affiliations should nullify their status as independents, Harvey said.

Stretton argued that Pennsylvania's law unconstitutionally creates an insurmountable barrier to candidates from fledgling third parties. "It's contrary to the whole political process," he said.

The Commonwealth Court said it expected to issue a ruling by Monday on Stretton's complaint that he has inadequate time to prepare as well as on Harvey's demand that Nader be stricken from the ballot because of his party affiliation.

In 2000, Democrat Al Gore won Pennsylvania, beating President Bush by 204,840 votes of 4.9 million cast in the state. Nader received 103,392 votes.

The Bush and Kerry campaigns both consider Pennsylvania important in the November election, because it is the fifth-largest electoral prize and because the results were so close in 2000. Recent statewide polls show Kerry with either a slight lead over or in a dead heat with Bush. Nader has been preferred by less than 5 percent of respondents in the pollings.