Sergio Witz Rodriguez was one ticked-off poet.

He thought nobody was solving Mexico's social and economic problems, least of all its politicians. So he worked himself into a righteous, lyrical lather and wrote a 21-line poem, saying, among other things, that he would like to use the Mexican flag as toilet paper.

The poem was published in a literary journal in 2001. That's when Witz, a father of three young girls, was arrested, fingerprinted, hauled before a judge and introduced to Chapter 5, Article 191 of the federal penal code, which calls for up to four years in prison for "insulting national symbols."

"This is absurd," said Witz, 42, a college literature professor in this Caribbean city on the Yucatan Peninsula. "I am not a threat to the state."

Now, after more than three years of legal proceedings that Witz described as Kafkaesque, his case may soon be heard by the Mexican Supreme Court in what legal analysts called one of the most important freedom of expression cases in recent memory.

The Mexican constitution guarantees free speech, as long as that speech doesn't injure someone else, provoke a crime or incite public disturbances. But federal law dating to the 1930s makes it illegal for anyone to insult national symbols, particularly the flag and the national anthem. The laws are vestiges of an era when presidents with vast power controlled the press and placed little importance on individual freedoms. Legal observers said the court may use Witz's case to determine the constitutionality of the law.

Since President Vicente Fox was elected in 2000, breaking the 71-year-rule of the Institutional Revolutionary Party, or PRI, he has called for greater guarantees for freedom of expression and the press. But analysts say that old thinking persists. Congress recently censured an artist for her "kitsch" depictions of the Mexican flag, and officials in several states have taken steps to curb free expression. One governor recently had two men jailed for a week for shouting insults at him at a public rally.

"We have yet to understand that democracy is based on freedom of expression," said Jaime Cardenas, a specialist in constitutional law at the National Autonomous University of Mexico in Mexico City. "The courts and authorities must learn to interpret things differently, to put freedom above other considerations."

The Witz case is similar to debates over flag burning in the United States. Some argue that people in a free society have a right to desecrate national symbols in protest, while others argue that attacking those symbols is a criminal act of disrespect. U.S. laws prohibiting the burning or defiling of the American flag have been ruled unconstitutional by the Supreme Court.

"By spreading his negative philosophy, he's destroying our values," said Abel Santa Cruz Menchaca, 63, a former military officer who filed the original complaint against Witz. Menchaca, whose father and grandfather were generals in the Mexican army, said Witz was "attacking something that gives us identity as Mexicans."

Menchaca said Witz has overstepped his rights by insulting other Mexicans. He said it was "dangerous" to publish such a poem, likening it to a passenger on a crowded boat urging other passengers to poke holes in the hull. "If we don't respect our laws, we are a nation of savages," Menchaca said.

Menchaca said that when he saw Witz's poem in Criterios magazine, he brought it to the attention of Carlos Justo Sierra, the local Interior Ministry chief. Sierra said he then filed a formal complaint with federal prosecutors. Sierra, 72, pointed to a photo on his office wall of his great-grandfather, a former ambassador to Spain, and had trouble controlling his temper as he discussed Witz.

"I'm from a family that has defended Mexico for more than 150 years," said Sierra, who is also a journalist and author. "So for me, statements against the values that symbolize my country are abominable."

He added: "Personally, I think Mr. Witz is trash."

In his breezy home in the city center, Witz sat in his small library where he keeps thousands of books carefully wrapped in plastic to guard against humidity. He said the whole episode had been bizarre, since the day two police officers came to the university to arrest him. Witz said he thought maybe someone was playing a practical joke, so he told the judge his only accomplice was God and suggested she issue an arrest warrant for the Almighty.

He said the judge was angry and aggressive, but eventually told him if he submitted a letter of apology to the court, the case would be dropped. At that point Witz -- "alias, Poet," according to court documents -- said he realized the judge was serious, and he began to see that important free speech issues were involved. He refused to send the letter, and he has appealed his case all the way to the Supreme Court. Justices are now deciding whether to hear it.

Witz, who has written six volumes of poetry, said the controversial poem, whose title contains an expletive, was not his best work. And he said it was published by accident: He meant to send the magazine a different piece. "It is ridiculous to try someone who wrote a few verses, when there are so many thieves, rapists and white collar criminals who go free," Witz said. "Freedom to say what you think is the greatest thing a writer can have . . . This is not just an aggression against me, but against freedom."

Sergio Witz Rodriguez was arrested after writing a poem suggesting the Mexican flag be used as toilet paper.Abel Santa Cruz Menchaca, left, a former military officer, filed the original complaint against Witz with Carlos Justo Sierra, an Interior Ministry official, who said, "I think Mr. Witz is trash."