New rules, new voters and a tight presidential contest combined to create "a recipe for problems," said Sean Greene, who was assigned to watch Cleveland polls for the Election Reform Information Project, a nonpartisan research group on election reform.

Nearly one in three voters, including about half of those in Florida, were expected to cast ballots using ATM-style voting machines that computer scientists have criticized for their potential for software glitches, hacking and malfunctioning.

Other major concerns were over provisional ballots, new this presidential election and a potential source of delayed counts, and whether poll workers were adequate and sufficiently trained.

In one Richmond, Va., polling place, voters were confronted with the wrong congressional race on the ballot the 7th District instead of the 3rd.

"Once it was discovered about 6:10, 6:15 (a.m.), people were offered a paper ballot," said Virginia Board of Elections executive secretary Jean Jensen. "I think the unknown is how many votes were cast before that happened."

Long lines greeted voters in many big cities in closely contested states: Fort Lauderdale, Florida, Columbus, Ohio, Detriot and elsewhere. Five locations in Franklin County, Ohio, opened up to a half-hour late because poll workers did not show up on time.

In Essex, Md., an election judge left a polling place briefly, saying he forgot something at home. Voters who had to wait were allowed to vote by provisional ballot.

One polling location in Mauldin, South Carolina, was forced to switch to paper ballots because of equipment troubles.

In Volusia County, Florida, a memory card in an optical-scan voting machine failed Monday at an early voting site and didn't count 13,000 ballots. Officials planned to feed and count those ballots Tuesday.

Chellie Pingree, president of the citizens lobbying group Common Cause, said she feared poll workers faced with long lines would be pressured to make quick but bad interpretations on rules governing registration validity and identification requirements.

"There's no question it's going to be a high turnout," Pingree said. "It's going to just add more confusion to already overburdened, understaffed polling places, many of which will have as many lawyers and poll challengers as they have people voting."

By mid-morning EST, an online and phone hotline maintained by nonpartisan and liberal voting-rights activists logged more than 1,650 items, mostly related to complaints or questions about registrations and polling locations. But some voters in New York and Pennsylvania complained to the hotline of troubles with non-electronic machines.