INDIANAPOLIS - In April 2006, a federal judge upheld Indiana's law on voter identification, the strictest in the nation, saying there was no evidence that it would prevent any voter from having his ballot counted.

But on Election Day last November, Valerie Williams became that evidence, according to lawyers in a case that will be argued before the Supreme Court on Wednesday. After Ms. Williams grabbed her cane that day and walked into the polling station in the lobby of her retirement home to vote, as she has done in at least the last two elections, she was barred from doing so.

The election officials at the polling place, whom she had known for years, told her she could not cast a regular ballot. They said the forms of identification she had always used - a telephone bill, a Social Security letter with her address on it and an expired Indiana driver's license - were no longer valid under the voter ID law, which required a current state-issued photo identification card.

"Of course I threw a fit," said Ms. Williams, 61, who was made to cast a provisional ballot instead, which, according to voting records, was never counted. Ms. Williams - who has difficulty walking - said she was not able to get a ride to the voting office to prove her identity within 10 days as required under the law, and her ballot was discarded.

The incident is at the heart of the highly anticipated case, which challenges the constitutionality of the Indiana law and, according to Daniel P. Tokaji, a professor of law at Ohio State University, is "the most important case involving the mechanics of election administration in decades."

The case goes before the Supreme Court just as the 2008 presidential primaries are beginning. The court will probably deliver its decision by late June, in time to affect the November elections.

Supporters of the law, most of them Republicans, say a requirement for state photo identification card is a prudent step toward curbing voter fraud. They say the requirement helps restore confidence in the voting process by removing the potential for fraud, though Indiana has never cited a case of "voter impersonation," which is what the law is supposed to prevent.

Opponents of the law, most of them Democrats, view voter identification requirements as a deterrent that disproportionately affects poor, minority and elderly voters, who more often than other people lack the required forms of identification and who also tend to back Democrats. And unlike supporters of the law, they say they have evidence to bolster their case and show that it has harmed Indiana voters.

A brief filed with the Supreme Court by the Marion County Board of Elections, the state's largest voting jurisdiction and a defendant in the case, said Ms. Williams - who is a black Republican - and 31 other voters had to cast provisional ballots because they showed up at the polls without the state-required ID, which can include a driver's license, a passport, a state-issued ID or some other government-issued photo identification. Because they also failed to appear later at county offices with the identification required to validate their identities, all of these voters had their ballots thrown out, records show. In interviews, many of these voters said they could not find transportation or could not afford the IDs.

All of these voters appeared at the polling place for the precinct in which they were registered, and all of the signatures on their provisional-ballot envelopes matched the appropriate poll book signatures. At least 14 of these voters had voted in 10 elections before last year, according to voting records.

Last year, legislators in 27 states proposed laws like the one in Indiana, seeking to increase identification requirements for registration or voting, according to Justin Levitt, a lawyer for the Brennan Center for Justice at the New York University School of Law. Mr. Levitt predicted legislative and legal battles in at least that many states, depending on how the Supreme Court ruled.

But the decision will affect more than just the voter-identification issue.

In the 1980s and '90s, the Supreme Court came up with a test for assessing any law that placed hurdles before voters. The justices ruled that courts must weigh the value of the law to the state against the burden it placed on voters.

How the court applies that test in this case could set the standard for challenges to election rules across the country. The decision could affect a range of other voting-related rules being imposed by states, including ones involving the handling of provisional ballots, new restrictions on voter registration and the methods states can use to purge voters from registration rolls.

Professor Tokaji, who was hired by the federal Election Assistance Commission to help produce a report released last year on voter-identification requirements , said that Arizona, for example, would study the court's ruling to see whether it could continue to require voters to present either one photo ID or two forms of nonphoto ID. Similarly, in Ohio, litigation is pending over such matters as how old a utility bill can be for a voter to use it as identification.

Supporters of the law said the requirement was hardly burdensome in today's society.

"It is exceedingly difficult to maneuver in today's America without a photo ID (try flying, or even entering a tall building such as the courthouse in which we sit, without one)," wrote Judge Richard A. Posner in a January 2007 opinion by the Seventh United States Circuit Court of Appeals in Chicago upholding the Indiana law and affirming a 2007 decision by Sarah Evans Barker, a federal district court judge. "And as a consequence, the vast majority of adults have such identification."

The Bush administration, arguing in favor of the law in a brief filed with the Supreme Court, suggested it was not necessary to prove fraud was actually taking place, given the importance of preventing such fraud.

"The state's interest in deterring voter fraud before it happens is evident from the monumental harm that can come from such fraud," the brief said.

Opponents of the law point to the three states - Georgia, Michigan and Missouri - where state officials have recently conducted the most systematic studies on the topic. Those states found that at least 4 percent of registered voters lacked the type of ID needed under the strictest voter identification laws. A 2007 study by political scientists at the University of Washington found that about 13 percent of registered voters in Indiana lacked the required identification.

Studies on whether voter identification laws affect turnout have come to different conclusions, some finding an impact, especially on members of minorities, and some finding no impact. All of the studies have acknowledged limitations on their conclusions given that strict photo ID requirements have only been in place in a few states for a few elections.

Only Florida, Georgia and Indiana require a voter to present photo identification to cast a regular ballot. Other states allow other types of documentation, like utility bills or a sworn affidavit from the voter. Twenty-three states in effect do not require proof of identification of all voters, requiring only what federal law demands: only first-time voters who apply by mail and have not otherwise been verified by the state must prove their identity with documentation.

Mary-Jo Criswell, 71, who - like Ms. Williams - an Indiana voter cited in the case before the Supreme Court, had her vote thrown out in November after she was told the identification she had used in previous elections - a bank card with a photograph, a utility bill and a phone bill - no longer sufficed.

"It was particularly galling for me since I was a former voting precinct committeewoman and I, of all people, should not be missing an election," said Ms. Criswell, who is a Democrat.

"It's like I'm having to recreate my identity and build a paper trail after all these years of never having problems," she said, explaining that her epilepsy had prevented her from ever getting a driver's license. Her passport expired in the 1950s, she said, and she did not have a copy of her birth certificate last November.

Since last November's election, she said, she has obtained a copy of her birth certificate but has still not gotten the required photo ID.

© 2007 The New York Times