Alan C. Kessler, a partner at Wolf Block in Philadelphia who recently hosted a $6 million fund-raiser for Mr. Obama, said he had already received four calls from Obama volunteers asking him to work on Election Day. Mr. Kessler said the 2000 election had caused many lawyers to want to become more active.

“Lawyers have always written checks,” Mr. Kessler said. “Now we are taking it to the next level in assuring that there will be no issues on Election Day. We are learning from the last two elections and we now have the credo ‘Never again.’ If we lose, we lose. But we don’t want it because of something that took place in the polling place.”

Some firms, like Saul Ewing in Philadelphia, are allowing their lawyers to receive pro-bono credit for voter protection work on Nov. 4. Saul Ewing, with 250 lawyers and offices in the mid-Atlantic region, says that lawyers from nearly all of its nine offices will work at the polls and that the firm’s Harrisburg office had been used for election training.

“Our lawyers are willing to go mano-a-mano if necessary,” said Orlan Johnson, a partner at Saul Ewing and a member of the Obama national finance committee. All volunteers must undergo a training session either in person or online with the Obama campaign.

“We’re going to have lawyers at the polls and in close proximity to the court houses,” Mr. Johnson said. As an example, he said lawyers could be helpful in keeping the polls open when lines became extremely long.

The McCain campaign and the Republican National Committee declined to say how many lawyers they had enlisted. Sean Cairncross, the committee’s chief counsel, said: “We will have enough lawyers to respond to any contingency. We have a great nationwide volunteer core of lawyers ready to help. On Election Day, we will be engaged at every level.”

Mr. Cairncross said Republican lawyers would be on the lookout for voter fraud, and would work to halt such previous stunts as having busloads of voters show up to keep polls open beyond their statutory closing time.