MEXICO CITY — More than a million people overflowed Mexico City's streets yesterday to protest the prosecution of mayor and presidential hopeful Andrés Manuel López Obrador.

Mexico City police estimated that 1.2 million protesters joined the so-called "March of Silence," which would make the protest the largest march for democracy in Mexican history. They wore white masks over their mouths and carried signs with the mayor's picture that read, "We are with you" and "You're not alone."

Opinion polls have given López Obrador a large lead in advance of Mexico's 2006 presidential election. López Obrador advocates reducing Mexico's dependence on the United States, criticizes free trade and emphasizes creating jobs for the 40 million Mexicans who live in poverty.

However, he's been in political limbo since April 7, when Congress voted to strip him of political immunity so he could be charged in a murky land-expropriation case.

Federal Attorney General Rafael Macedo de la Concha charges that López Obrador disobeyed a March 14, 2001, court order to stop building an access road to a hospital. A conviction would torpedo his presidential campaign, and delays in the case could prevent him from registering as the Democratic Revolutionary Party's (PRD) presidential candidate before a January deadline.

The mayor denies the charge, and Macedo suffered a setback on Friday, when a judge sent charges of abuse of authority back to the attorney general, who said he would refile the case.

The huge, peaceful rally on a sunny, hot day suggested that the mayor's political momentum is growing, at least for now.

Led by the mayor, demonstrators met at the golden statue of the Angel of Independence in downtown Mexico City's wide Reforma Avenue and joined thousands of other protesters at the city's main plaza, the Zócalo, where the mayor announced to thunderous cheers that he was returning to work today. Officials of Macedo's office have said they would arrest him if he tried to report for duty at his office.

"The case is dead," enthused the mayor, who has already begun his presidential campaign in several states.

Marchers set off fireworks, threw confetti and waved giant banners showing President Vicente Fox and other political leaders in black-and-white-striped jail suits. Many urged Fox to resign.

Fox has said the case isn't political but a legal procedure to show that he meant it when he said that no one was above the law.

Most people interviewed yesterday, however, said the case against López Obrador is a political plot to prevent him from running for president. Opinion polls consistently show a similar sentiment.

Information from the Los Angeles Times is included in this report.