WASHINGTON (Reuters) - New laws in 10 states requiring voters to show photo identification will make it more difficult for millions of Americans to cast ballots and likely will drive down turnout among minorities, the poor and elderly, a study said Wednesday.

The Brennan Center for Justice at New York University Law School said that one in 10 Americans lack the necessary government-issued photo IDs that now are required in Alabama, Georgia, Indiana, Kansas, Mississippi, Pennsylvania, South Carolina, Tennessee, Texas and Wisconsin.

Most of the new laws were passed by Republican-controlled legislatures, and the voting blocs that analysts say the laws are most likely to affect typically favor Democrats.

About one-quarter of African Americans, 16 percent of Hispanics and 18 percent of Americans over age 65 do not have the type of ID that the voting laws require, the Brennan Center report said.

"These new laws will make it more difficult for millions of Americans to vote," said Larry Norton of the Brennan Center's Democracy Program. "The idea that we're forcing certain people to go through these very difficult extra hoops is antithetical to some of the founding principals of this country."

The report said that more than 10 million eligible voters live more than 10 miles from the nearest full-time state ID-issuing office. About 500,000 of them do not have access to a vehicle, and most live in rural areas with limited public transportation, the report said.

A BACKLASH FROM 2008?

"What this report demonstrates is the potential impact on voters and possibly some potential impact on the upcoming election," said Keesha Gaskins, a co-author of the report. "We really are talking about a population of individuals that really could influence the outcome."

The states with restrictive voter ID requirements account for 127 electoral votes -- nearly half the 270 needed to win the presidency -- in the November 6 presidential election between Obama and Republican candidate Mitt Romney.

A separate study released this week by the National Urban League said that even a small drop in turnout by African Americans, whose overwhelming support for Obama helped him win election in 2008, could have a big impact in several key states in November.

The National Urban League, a civil rights group, has claimed that the new voter ID requirements pushed largely by Republicans were a response to the high voter turnout among Democrats in 2008.

Conservative groups and Republican-led legislatures that have backed the new rules say they will help ensure fair voting and reduce fraud.

They also dismiss claims that it is difficult for many people to travel to get a photo ID, saying it is similar to finding a way to get to the polls on Election Day.

A QUESTION OF ACCESS

But rights groups and the Brennan Center, which has joined in lawsuits in several states to oppose the laws, say the new rules unfairly target minorities and low-income voters.

The new report described how state-run ID offices are open at irregular hours, such as one in Wisconsin that is open only on the fifth Wednesday of every month even though there are only four months of the year that have five Wednesdays.

In Alabama, Georgia, Mississippi and Texas, the report said, many ID offices are open only part-time in areas with relatively large populations of blacks and Hispanics.

States with such laws are required to provide free photo IDs to eligible voters who do not have one, but the costs of obtaining birth certificates and other needed documentation, along with travel to the ID office, make it difficult for some voters, the report said.

Many of the new laws are being contested in court. A panel of federal judges last week finished hearing arguments about Texas' law by questioning the state's attorney over whether minorities are unfairly hurt by the requirements.

Rights groups and the Obama campaign also are challenging various laws that change rules for early, in-person voting in the days before Election Day. The Obama campaign filed a lawsuit in Ohio this week to block a Republican-backed law that stops in-person early voting three days before election day for most Ohioans.

At a Romney campaign event in Ohio, Republicans dismissed claims that the law will discourage Ohio voters from going to the polls.

"The other side of the aisle is talking about access to voting," Ohio state Representative Randy Gardner said in Bowling Green. "Voters will have 784 hours to vote. There's no partisan divide here ... Every Ohioan who wants to vote will freely and clearly have that right."

(Additional reporting by Sam Youngman in Bowling Green, Ohio; Editing by David Lindsey and Cynthia Osterman)