With millions of new voters heading to the polls this November and many states introducing new voting technologies, election officials and voting monitors say they fear the combination is likely to create long lines, stressed-out poll workers and late tallies on Election Day.

At least 11 states will use new voting equipment as the nation shifts away from touch-screen machines and to the paper ballots of optical scanners, which will be used by more than 55 percent of voters.

About half of all voters will use machines unlike the ones they used in the last presidential election, experts say, and more than half of the states will use new statewide databases to verify voter registration.

With Senator Barack Obama’s candidacy expected to attract many people who have never encountered a voting machine, voting experts and election officials say they are worried that the system may buckle under the increased strain.

“I’m concerned about the weak spots,” said Rosemary E. Rodriguez, the chairwoman of the United States Election Assistance Commission, which oversees voting. “So much depends on whether there will be enough poll workers, whether they are trained enough and whether their state and county election directors give them contingency plans and resources to handle the unexpected.”

Some areas, including Baltimore, ran out of paper ballots either in 2006 or in this year’s primaries and plan to order many more this fall.

Ohio plans to add paper backups in case its electronic machines break down again, as they did in 2004, creating long lines. New Jersey, New York and California, among other states, face shortages of poll workers or the money to pay for them.

Voting rights advocates are working with officials in Florida, Missouri, Ohio and Pennsylvania to try to prevent the kind of ballot design problems that added to the loss of around 12,000 votes in this year’s presidential primary in Los Angeles County and 18,000 votes in a 2006 Congressional race in Sarasota County, Fla.

As state and local election officials scramble to get enough ballots, workers and equipment to handle the predicted high turnout, many are trying to ease the strain of Election Day by encouraging voters to cast their ballots early. But the problems may be complicated by changes to the lists of eligible voters. Recent purges of voters from registration lists and the influx of registrations may result in names erroneously being dropped and eligible voters showing up at the polls to find their names not on the rolls. (Advocacy groups have encouraged voters to check their registration with election officials at least two weeks before the polls open.)

“Election officials are unanimous in their commitment to ensuring every eligible American’s right to vote, but in many places the system they oversee simply isn’t designed to handle anywhere near the number of voters that may turn out,” said Doug Chapin, director of electionline.org, a project of the Pew Center on the States. “In previous elections, the question has been, ‘Will the system work for each voter?’ But this year the real question is whether the system can handle the load of all these voters.”

Poll worker training and ballot design will be more important than ever this year. The election commission has predicted that at least two million poll workers will be needed in November, double the number in the 2004 presidential election. In New Jersey, election officials placed advertisements in newspapers asking people to sign up to work the polls. In California, election officials posted pleas on the Internet.

But many states face budget problems that make it hard to recruit poll workers. New York City election officials have said they lack the money to pay the estimated 8,000 additional poll workers needed in November. Several states have resorted to recruiting high school students.

Ms. Rodriguez said that the high level of turnover in the people who run state and local elections was also a concern. More than two-thirds of the election directors in the nation’s 50 largest counties were new to the office in 2004, and the number may be even higher now, according to Election Data Services, a Washington consulting firm that tracks voting trends.

Many voters heading to the polls in November will receive a paper ballot for the first time. The ballots are counted by optical scanners and provide a more reliable paper trail than touch-screen machines in case of a dispute or a malfunction.

A third of voters will use touch-screen machines, down from 38 percent in 2006, while about 55 percent of voters will use paper ballots read by optical-scan machines, up from 49 percent of voters in 2006, said Kimball W. Brace, president of Election Data Services.

The main issue with the paper ballots will be their unfamiliarity to voters, not the technology itself. Ideally, in fact, paper ballots could reduce lines at polling places, because election officials would not have to set up a limited number of expensive touch-screen machines in each booth. Paper ballots require only a writing surface, and far fewer optical-scan machines are needed to count them.

But poll workers will have to explain the system to new voters and make certain to print and distribute enough paper ballots for each polling place. In the past, shortages of paper ballots or electronic machines have been a common cause of long lines and people leaving the polling places without voting, said Adam Fogel, a program director at FairVote, a voting rights advocacy group.

“For us, the issue isn’t what type of machines will be used but how they are distributed,” Mr. Fogel said.

He said election officials must be nimble enough to send extra ballots or machines to precincts experiencing heavy turnouts. But a report to be released in August by FairVote says that many swing states have been unable to do that.

The swing states that experienced the longest lines, including Florida, Michigan, Missouri, Ohio and Pennsylvania, lack uniform rules for distributing machines and ballots, the report says. Most states allocate machines and ballots in August, two months before most of the major registration drives are completed, according to the report.

“Allocating enough ballots and machines is a tricky science under any circumstances, but especially when turnout is proving to be so unpredictable,” said Tova A. Wang, vice president for research at Common Cause, a voting rights advocacy group.

In Baltimore, election officials so underestimated turnout in the 2006 primary that polling places ran out of ballots by midday and voters ended up using random pieces of paper, including campaign literature, as ballots, she said.

In Albuquerque, on the other hand, voting officials overestimated turnout in the primaries last month and had to shred more than $1.2 million worth of unused ballots, Ms. Wang said, adding that states should probably still err on the side of ordering more, not fewer.

Although most of the 30 states with touch-screen machines still do not plan to provide backup paper ballots, others, including Ohio, will do so for the first time in a presidential election. In 2004, hundreds of voters in Knox County, Ohio, many of them Kenyon College students, had to wait more than nine hours after one of the two voting machines at their polling place just off campus broke down. There were reports of lines where the wait was several hours long in at least three other counties.

“We refuse to let that happen,” said Jennifer L. Brunner, the Ohio secretary of state, who plans to instruct all counties that use touch-screen machines to order backup paper ballots equal to at least a quarter of the votes cast there in the last presidential election.

Ohio now permits no-fault absentee voting, Ms. Brunner said, which means voters no longer have to provide an excuse to cast an absentee ballot, either in person or through the mail starting 35 days before Election Day.

Thirty other states permit no-excuse absentee voting and a third of voters nationally are expected to vote early or absentee in the next election, experts say.

Larry Norden, a lawyer with the Brennan Center for Justice at New York University School of Law, said he was concerned with the design of this year’s ballots. Too often, Mr. Norden said, voters are confused by ballots with instructions written in unclear legal jargon, lists of candidates that span more than one column, boxes that can be checked on either side of a candidate’s name, or vague borders that fail to distinguish one electoral contest from another.

“The bottom line is that new voters are more prone to mistakes caused by confusing ballots,” Mr. Norden said. “We’re expecting a lot of new voters in November.”

Jonah H. Goldman of the Lawyers’ Committee for Civil Rights Under Law said the high turnout and surge of new voters were likely to cause bottlenecks as eligible voters arrive at the polls and find their names are missing from the databases that election officials are using to check registration.

In the primaries, reports from at least 12 states said eligible voters ran into that problem.

The new computerized databases, required by a 2002 federal law, were meant to provide uniformity in how states run elections. By coordinating with other state lists, officials can more easily remove from the rolls people who have died, changed residence or been convicted of felonies, to help reduce fraud. But the purges also occur with little oversight, and errors can be significant.

Mr. Goldman said his organization was closely watching Florida, Georgia, Louisiana and Mississippi, because those states have purged hundreds of thousands of voters since 2006.