FACTBOX-U.S. voting rules are a hodgepodge

(Reuters) - The United States allows citizens age 18 and up to vote, but elections are run by the individual states under rules that vary widely. Even within the states, voting technology and procedures can vary from county to county.

Here are some factors that could lead to disputes in the November 4 presidential elections:

-- VOTER REGISTRATION - A handful of states have same-day registration while most close the books a month or so before election day. Same-day registration can boost turnout but critics say it leads to fraud because there is no time for verification.

Federal law requires states to purge the lists of those who have died or moved away. Some do that by disqualifying voters who fail to respond to official mailings or by eliminating those whose data does not perfectly match that on other government databases such as driver's licence or Social Security records. Critics complain that a single typographical error can lead to disenfranchisement.

Some states automatically restore convicted felons' voting rights after they have served their sentences while others require a cumbersome restoration process. In the latter states, some law-abiding voters have said they were purged from the rolls because their names were similar to those of convicts.

Both major parties have conducted drives to register large numbers of new voters and each has accused the other of submitting bogus registrations. Election supervisors say those are usually weeded out, and that nonexistent people can't show up at the polls anyway.

-- VOTER IDENTIFICATION AT THE POLLS - By federal law, first-time voters must present valid identification before casting a ballot, typically a driver's licence or other government-issued identification with their photo. States are free to adopt additional requirements and many do. There is often confusion among voters on what is required. Some voters are deterred by false reports that they will be blocked from voting if an identity check shows they owe taxes or have unpaid parking tickets.

-- POLLING STATION SNARLS - These can vary from machines failing to boot up, unusually high turnout, failure to hire enough poll workers or failure to provide enough voting booths. Voters still waiting in line at the official closing time are usually allowed to cast ballots, but states and counties decide whether to extend voting hours.

-- VOTING MACHINES AND VOTE COUNTING - Close votes lead to questions over whether every vote was counted and to recounts -- most famously in Florida in 2000 when an extremely close final vote tally delayed the result of the White House race between George W. Bush and Al Gore. States or local districts decide what technology is used, and 24 states use electronic voting machines or lever-operated machines. Those using paper ballots often use electronic scanners to count them.