WASHINGTON » The nation’s voter registration rolls are in disarray, according to a report released Tuesday by the Pew Center on the States. The problems have the potential to affect the outcomes of local, state and federal elections.

One in eight active registrations is invalid or inaccurate. At the same time, 1 in 4 people who are eligible to vote — at least 51 million potential voters — are not registered.

The report found that there are about 1.8 million dead people listed as active voters. Some 2.8 million people have active registrations in more than one state. And 12 million registrations have errors serious enough to make it unlikely that mailings based on them will reach voters.

"These problems waste taxpayer dollars, undermine voter confidence and fuel partisan disputes over the integrity of our elections," said David Becker, director of election initiatives at the center.

Becker warned that poor record keeping at the registration stage is not evidence of fraud at polling places.

"These bad records are not leading to fraud but could lead to the perception of fraud," he said.

What seems clear is that many people who are eligible to vote and want to do so fail because of flaws in the registration rolls. In 2008, roughly "2.2 million votes were lost because of registration problems," according to a report from the Voting Technology Project of the California Institute of Technology and the Massachusetts Institute of Technology.

Heather Gerken, a law professor at Yale, said the Pew report quantified and illuminated just how poorly the election system manages its most fundamental task.

"Until Bush v. Gore, election administration was the dirty little secret ofB elections," she said, referring to the Supreme Court decision that delivered the 2000 election to George W. Bush after poorly run elections in Florida. "And registration has always been the dirty little secret of election administration."

The flaws in the voter registration rolls have a disproportionately negative impact on mobile populations, including students and other young people, the poor and members of the military, the Pew report found.

"It’s not clear that it has a uniform partisan effect," Nathaniel Persily, a law professor and political scientist at Columbia, said of those findings. But he added that "it is now pretty clear that Democrats want to enact measures that make voter registration easier, and Republicans fear that would be an invitation to fraud."

The Pew report compared state voter registration lists with a database maintained by Catalist, a company that collects and sells information about voting-age Americans based on data from public and commercial sources.

The United States differs from most other modern democracies in relying on a decentralized election administration system that places the burden of registration on voters rather than treating registration as a government responsibility.

"Part of the problem is that it is difficult for us to be proactive," said Linda H. Lamone, Maryland’s administrator of elections. "We have to rely on the voters."

In Argentina, Australia, Belgium, Germany, Peru and Sweden, by contrast, the national government maintains its own registries of citizens eligible to vote, according to a 2009 report from the Brennan Center for Justice.

Gerken said the difference between U.S. and international practice helps explain many of Pew’s findings.

"Everyone else in a modern democracy does it better," she said, adding that the U.S. system "is a silly way to run a railroad."

It is also expensive. In 2008, for instance, Oregon spent $4.11 per active voter to process registrations. A 2001 study from the voting project found that local election offices spent a third of their budgets on registering voters.

Canada, by contrast, spent less than 35 cents per voter to process registrations — and 93 percent of eligible voters there are registered.

The registration process in the United States often involves handwritten forms, some collected by third parties. Those forms are then manually entered into an electronic system, a process bound to introduce flaws.

People who move, moreover, often take no steps to inform administrators at their old addresses, and a new registration does not typically result in a notification to cancel the previous one. Yet a quarter of all voters assume that their registrations automatically move with them, the report found.

As a consequence, active registrations in two states are common. Some 70,000 people are registered to vote in three or more states.

This is also a consequence of a distinctively U.S. approach.

"The United States is unique both in its requirement that voters re-register each time they move and in the high mobility of the population," Persily and Stephen Ansolabehere, a professor of government at Harvard, wrote in a 2010 article, "Measuring Election System Performance," in The New York University Journal of Legislation and Public Policy.

One possible response, employed in Arizona and Washington state, is to allow online registration, which is cheaper, more accurate and more convenient but may raise security concerns. Lamone, the Maryland election official, said her state for now "is completely paper-based" but would allow online registration starting in July for people with a valid state driver’s license or military identification.

The Pew report urged administrators to make greater use of data-matching technologies commonly used by private businesses and to look to government resources like motor vehicle records, Social Security death records and the Postal Service’s change-of-address database.

In an interview, Persily proposed what he called an easy fix to many of the problems identified in the new report. The Postal Service’s change-of-address form, he said, could include a box that, when checked, would generate a cancellation notice directed to the old voting place and a registration request to the new one.