Seated at twin computer terminals in the City-County Building in Downtown Pittsburgh yesterday, lawyers for Ralph Nader and the Democrats challenging his Pennsylvania nominating petitions were locked in a line-by-line slog through the signatures he submitted in August to get on the ballot.

The painstaking review was one of several similar exercises across the state.

Reversing an earlier Commonwealth Court decision against Nader's candidacy, the state Supreme Court sent the case back to Commonwealth Court last week and ordered scrutiny of the more than 50,000 signatures submitted by the Nader campaign.

The challenging attorneys maintain that more than half the signatures are invalid for one reason or another -- some because they did not come from a registered voter, others because they are duplicates or because the signature or address does not conform to the dictates of state law.

By early yesterday, the Allegheny County portion of the review had made its way through roughly 5,000 of the 8,700 signatures collected in the county.

Mark Wolosik, director of the county elections division, said the attorneys might not complete the process until tomorrow. At that point, the court is expected to hold a hearing on the validity of the signatures that remain in dispute.

It is expected to be late in the week before the court could hope to consolidate the results of the scattered proceedings around the state.