Democrats attempted to put a roadblock in front of independent candidate Ralph Nader's efforts to gain access to the presidential ballot in Arizona, with the filing of a lawsuit by two Arizona residents challenging the validity of the petitions submitted by Nader's campaign.

The suit underscores the determination of the Democrats to try to frustrate Nader's efforts to qualify for state ballots. It is a shift from four years ago, when party officials and the campaign of Vice President Al Gore generally ignored Nader, who was running as the Green Party candidate, in the hope that his campaign would not attract support.

The suit, filed in superior court in Maricopa County in Phoenix, charges that, of the 21,512 signatures on Nader's petitions, only 6,045 are valid. State law requires Nader to submit 14,694 valid signatures to qualify for the ballot.

Although state law prohibits a political party from filing or financing such suits, the state party provided space in its office for volunteers and staff members working on their own time to review the signatures.

"We did this on our own," Arizona Democratic Party Chairman Jim Pederson said. "I hasten to say we're not taking action on behalf of the Democratic National Committee or the Kerry campaign."

Nader called the suit "potential harassment" and said if Democrats persist, he will revise his campaign strategy. "We will concentrate only on the close states."

The action in Arizona came a day after Nader stormed out of a Capitol Hill meeting in which members of the Congressional Black Caucus told him to abandon his bid for the White House. The chairman of the group, Rep. Elijah E. Cummings (D-Md.), refused to apologize for a meeting that Nader publicly described yesterday as abusive.

"Some of them used very abusive language," Nader told National Public Radio host Tavis Smiley during his morning program. "Congressman [Melvin] Watt of North Carolina used such abusive language until I could hardly believe what he was saying."

"We could understand his right to run, but we were just convinced after the meeting that this was just about Nader," Cummings said. "First of all, he can't win, but he can be an aider and abettor of four more years of President Bush's regressive leadership."