Lawyers for both parties are descending on key swing states, anticipating legal challenges in the wake of what could become a razor-thin decision that rests on how, where, and which ballots are counted. Such disputes could provide a coda to an election cycle that has been marked by state moves to limit early-voting days and require voters to provide photo IDs.

In one scenario already generating angst, small county election boards could determine the next White House occupant, with lawyers from both sides hovering over every decision in a replay of the 2000 election.

“We’re getting all kinds of lawyers,” said William A. Anthony, Jr., director of the board of elections here in Franklin County. “You got voting rights groups, groups on the right, groups on the left. Some have been here awhile; some come out of the woodwork. They’ll all file lawsuits.”

The legal maneuvering is already starting.

On Sunday in Florida, a judge extended early-voting hours in several counties after the state Democratic Party filed a lawsuit because lines were too long on Saturday for some voters to cast ballots — or, in the case of a precinct in Orlando, voting was shut down for several hours because of a suspicious package.

At one point on Sunday, election officials in Miami-Dade County locked their doors and shut down voting an hour into what was supposed to be a four-hour voting period, according to the Miami Herald. The decision was later reversed, and voting proceeded.

Florida relied heavily on early voting in 2008, but the Legislature limited the number of days this year, leading to massive waits and long lines over the weekend.

Late on Friday in Ohio, Secretary of State Jon Husted, a Republican, issued a new directive telling election boards not to count provisional ballots if a section that is supposed to be filled out by poll workers is left empty. Federal law allows voters to cast provisional ballots when their identity or polling place is uncertain on Election Day.

Attorneys for the Northeast Ohio Coalition for the Homeless are challenging the directive in federal court, saying that it is the poll workers’ responsibility — not the voters’ — to ensure that provisional ballots contain all needed information.

And on Sunday night, the Republican National Committee sent a letter to the Iowa secretary of state asking him to investigate news reports that Democratic operatives encouraged elderly voters to fill out and sign absentee ballots for other family members.

If the election is close, it could mean that the campaigns that have fought on the airwaves, on the debate stage, and door-to-door would turn to more technical arguments in courtrooms and before county election boards.

Steering Romney’s legal strategy would be Benjamin Ginsberg, a Washington-based attorney who has been close to him for years, and guiding Obama’s would be Robert Bauer, who has advised Obama since he came to Washington in 2005. Both would probably employ strategies that have grown more advanced in the aftermath of recounts like the 2000 presidential race in Florida.

“The analogy to warfare makes sense; the Pentagon is always improving its weaponry,” said Edward B. Foley, an Ohio State University law professor and an expert on election law. “Something of the same thing is going on in the legal battles. You just accumulate experience and sophistication in how to think about what to do.”

The popularity of early voting, and the limits that states have put on it, have led to long lines, including in Ohio, where on Sunday night there was a festive atmosphere at the one location where voters could cast early ballots in Franklin County.

A gospel choir sang. One man dressed up as Abraham Lincoln, several others as Sesame Street characters. Voters waited for an hour and a half in a massive line that snaked out the door of a now-vacant Kohl’s that is serving as a voting site.

There were at least four nonpartisan poll watchers standing outside to help anyone who had problems. Inside, the campaigns had designated observers.

“I’m here because this is the center of where everything is happening,” said Mary Jane Rosenfeld, who flew from Beaufort, S.C., to stand outside Ohio polling locations. “I wanted to make sure everything goes as they are supposed to be.”