SORGUES, France — A T-shirt worn by a 3-year-old nursery-schooler named Jihad has led to an unusual and politically charged criminal trial here that tests the limits of free speech — and common sense — in a France increasingly ill at ease with its growing Muslim population.

“I am a bomb,” the shirt said on the front. The back read, “Jihad Born Sept. 11.”

The prosecution and the defense both have predicted that the outcome is likely to become a legal precedent as the government and justice system handle recurring friction between France’s 8 percent Muslim minority and the majority of the country’s 65 million inhabitants who recognize their roots in an ancient Christian tradition.

The tensions have been increasingly visible as French soldiers combat Islamist guerrillas in Mali, in northwestern Africa, and anti-terrorism police scour the country’s poor suburbs in search of Muslim youths drawn by the call to jihad or revenge.

An Islamist cell broken up in nearby Marignane earlier this month, for instance, was preparing to construct bombs for terrorism attacks in French cities, authorities declared. In another sign of the strain, France’s highest court, the Cour de Cassation, last week overturned a lower-court decision that endorsed the firing of a nursery school teacher who refused to remove the Islamic veil covering her hair.

The case in Sorgues, a small town just north of Avignon, where Pablo Picasso and Georges Braque pursued their cubist art, began Sept. 25 at an unlikely place: the Ramieres de Sorgues municipal nursery. As she dressed the children after a lunch break, a teacher there became alarmed when she saw Jihad’s T-shirt.

Although little Jihad was, in fact, born on Sept. 11, the teacher saw an outrageous reference to Islamic war and the al-Qaida terrorist attacks on the United States on Sept. 11, 2001, in which nearly 3,000 people were killed. Concerned, she spoke with the principal, who was equally upset and called in Jihad’s 35-year-old Moroccan-born mother, Bouchra Bagour.

Told of the indignation produced by Jihad’s shirt, the single mother, who works as a secretary, apologized for causing trouble and said she had no intention of conveying a political message via her toddler. The shirt, she pledged, would be put away for good.

But the issue did not rest there. The principal wrote a report to school district authorities. A copy of the report landed on the desk of Mayor Thierry Lagneau. The mayor, from the conservative Union for a Popular Movement (UMP) party, said in an interview that he regarded the T-shirt as a “provocation,” and he immediately stepped into action.

“I said to myself, we can’t let that go by,” Lagneau recalled. “I didn’t know what was behind it, but we could not let that go. We have to impose limits.”

Lagneau wrote a letter Sept. 29 to the region’s chief prosecutor, Bernard Marchal, asking for an investigation for possible criminal prosecution as well as a “thorough” investigation by child-welfare authorities to see if Bagour was a fit mother. If Jihad showed up again in the T-shirt, the mayor warned, the principal had orders to turn him away, “given the attitude of his parents, who cannot decently ignore the dramatic impact of their acts.”

Before long, Bagour and her brother, Zeyad Bagour, 29, were called in separately by national police and questioned about their religious and political leanings. The mother was questioned for about an hour and released. The uncle, who had bought the T-shirt in nearby Avignon and given it to Jihad, said he was kept in custody for four hours, including more than two hours in a holding cell.

“The questions were scandalous,” said Soliman Makouh, Zeyad Bagour’s lawyer.

Zeyad Bagour, who was born in France and works nights in a fast-food restaurant, said in an interview that he was asked whether he practiced his Islamic faith ardently, whether he was interested in Islamist terrorism and whether he had traveled to Afghanistan or similar countries for contacts with jihadist organizations. His only recent foreign travel was to Ibiza for a beach vacation, he said he replied.

The most troubling question from police, Makouh said, was put to the mother as well as the uncle: Did Bagour induce labor three years ago, so Jihad would be born on Sept. 11? The answer from both was no.

After the police investigation, no terrorism-related charges were brought. But the prosecutor decided to charge Bagour and her brother with “apology for crime,” which under a 1981 French law carries a penalty of up to five years in prison and a $58,000 fine.

“Our society cannot tolerate extremist or equivalent attitudes,” Lagneau said at a news conference after the charges were lodged. “I am convinced that all those who have authority must act, denounce, show the greatest firmness. This, I believe, is our duty. Otherwise we would risk trivializing facts that are serious and recognized as such by the prosecutor.”

Zeyad Bagour, a bachelor who lives with his sister and two other siblings, said he had trouble understanding what the fuss was about. He bought the shirt without thinking of any political message, he said. The front already had the words “I am a bomb” printed on it, but he understood that as an expression roughly equivalent to “I am a real looker.” As for the back, he said, he just wanted to put down his nephew’s name and date of birth.

“I did it on a lark,” he recalled, apologizing for any alarm he may have raised. “It wasn’t even meant as a joke.”

For Lagneau, however, the T-shirt was more than a joke, even an ill-considered one; it was a deliberate call to Islamist jihad. He hired a lawyer and joined the criminal prosecution, making the city what is known in French law as a “civil party,” claiming to have suffered from an alleged crime.

“They knew very well what they were doing,” he said. “There is no ambiguity possible.”

At a four-hour trial March 6, Deputy Prosecutor Olivier Couvignou also portrayed the T-shirt as a deliberate political message. “There is nothing innocent in these words,” he said, according to news accounts of the proceedings. He asked the judges to impose a fine of $4,000 on the uncle and $1,300 on the mother.

Claude Avril, Lagneau’s lawyer, asked for roughly the same amount but has since dropped his request to a symbolic one euro, according to the mayor. In any case, the main punishment, in case of a conviction, would be a criminal record that would make getting a job difficult and would probably land Bouchra and Zeyad Bagour on watch lists in airports around the world, Soliman pointed out.

Soliman and Bouchra’s lawyer, Gaele Guenoun, argued that neither defendant was a militant and neither intended to broadcast a political message. The T-shirt was a private affair, they pointed out, meaning it did not correspond to the legal definition of “apology for crime.”

After hearing the arguments, the court took the case under advisement and promised to hand down its verdict April 10.

Makouh said Lagneau was acting out of political interest, currying favor among anti-immigrant voters for municipal elections scheduled next year. Although a conservative, Lagneau faces a challenge from the far-right National Front. The front is strong among the 18,500 residents of Sorgues, and its rising star, Marion Marechal- Le Pen, is considering a run for mayor, Soliman said.

“This area is like Mississippi in the United States during the civil rights struggle,” he said.

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