INDIANAPOLIS

Poor, black and elderly people tend to be less likely than others to have the photo identification required to vote under Indiana law, opponents of the law said Tuesday, citing a survey of prospective voters.

Democrats, too, are less likely to have the right ID, said the foes who filed a legal brief Tuesday in an effort to persuade the Supreme Court the law is unfair and should be overturned. The court will hear arguments in the case early next year, in the middle of the 2008 election campaign.

The state has defended the law as a way to combat voter fraud. Opponents say it unfairly targets poor and minority voters, without any evidence that voter cheating is a problem in Indiana.

"The alleged ill that this is out to correct doesn't really exist," said Justin Levitt, counsel for the Brennan Center for Justice at the NYU School of Law, which filed a brief arguing against the law. "There's no real justification for putting these people through this."

The survey, led by a researcher at the University of Washington, found that 86 percent of white eligible voters had current, valid photo identification, compared to 73 percent of black eligible voters.

While many people have driver's licenses or other identification, the study confirmed that many others don't, said researcher Matt A. Barreto.

"It is a very significant issue and one that most people take for granted," he said.

Politics was also found to be a factor. About 41 percent of those who have valid identification said they were Republican, while 32 percent were Democrats. Of those without ID, 34 percent were Republican and 38 percent were Democrats.

Among registered voters in Indiana, nearly 91 percent of those between 55 and 69 had a current ID, compared with about 80 percent of people 18-34 and about 84 percent of those over the age of 70. About 88 percent of registered voters making at least $40,000 a year had current ID, compared with about 82 percent of those making less than $40,000 a year, the study found.