One of Union Square’s regular orators, Geoffrey Blank, uses a megaphone to hold forth on his favorite topics such as Lenin’s theory of imperialism and his certitude that the American government orchestrated the destruction of the World Trade Center.

These days, Mr. Blank is directing his rhetoric not toward passersby but at Judge James Gibbons of the Criminal Court in Manhattan.

Yesterday, Mr. Blank, who is acting as his own attorney, delivered what is likely his final speech to Judge Gibbons as he attempted to have overturned a guilty verdict relating to three arrests for using his megaphone in public without a permit.

The courtroom comes with rules not enforced in Union Square, and Mr. Blank was allotted 80 minutes to argue that the megaphone ordinance violates the First Amendment.

The time constraint appeared to vex Mr. Blank, who interrupted Judge Gibbons to say: “With all due respect, does the time you talk count?”

“Yes,” the judge said, “the time I speak counts against you.”

“Oh, no,” Mr. Blank replied, before saying the police never had the authority to arrest him, nor District Attorney Robert Morgenthau the authority to prosecute him, nor the court jurisdiction to hear the charges.

In street-corner fashion, Mr. Blank drew from a range of sources: the Gospel, Fidel Castro, Thurgood Marshall, the Passover liturgy, and the First Amendment.

“This case is not about a guy who wants to speak in Union Square on a megaphone,” Mr. Blank, who is head of a group called the No Police State Coalition, said. “It’s about free speech. This is not about me but about vindicating the First Amendment.”

After listening closely to Mr. Blank’s speech and peppering him with questions, Judge Gibbons upheld the constitutionality of requiring permits for megaphone use. Mr. Blank has never applied for such a permit.

Union Square is “a speaker’s corner, always has been,” Judge Gibbons said. Nonetheless, regulating noise is, “especially in New York City, a key government interest,” he said.

Mr. Blank, 32, works as a lifeguard for the federal government in the Jacob Riis Park in Queens. He also is pursuing a master’s degree in sociology at Brooklyn College.

The arrests occurred between 2003 and 2004, when Mr. Blank would travel into Manhattan three times a week to give speeches, sometimes attracting scores of listeners. His arrests began over his lack of a permit for his megaphone, but the charges grew more serious as the police accused Mr. Blank of resisting arrest, striking back at officers, and attempting to incite riots as he was handcuffed.

In an interview, Mr. Blank’s brother, Jason Blank, said he has written to the governments of North Korea, Cuba, Belarus, and other countries to alert them to what he says is America’s political prosecution of his brother. Only Belarus has replied, Jason Blank said.

Last year, a jury convicted Mr. Blank of two counts of resisting arrest and of using a megaphone without a permit. He was not convicted of assault or inciting a riot.

Judge Gibbons spared the defendant any jail time and imposed no sentence except for a mandatory fine.

“I’m just your judge, and being a judge doesn’t make it appropriate for me to psychoanalyze you,” he said. “But my impression is that you are someone who loves attention. I can put it more favorably: You are someone who loves glory.”

Mr. Blank’s father offered a different assessment.

“Oh yeah, he’s stubborn,” John Blank said in a telephone interview Sunday. When his son was 5, “he put a hairpin in a socket and got shocked,” Mr. Blank said. Although John Blank blocked the outlets with plastic covers, he said, young Geoffrey shocked himself again.

“That about summarizes it,” Mr. Blank said.

More than 30 supporters, including the disbarred attorney Lynne Stewart, were present yesterday in support of Mr. Blank.

An assistant district attorney, Christian Browne, had asked that Mr. Blank receive six months incarceration.

“His actions may be explained by views held by the defendant about free speech,” Mr. Browne said of Mr. Blank. But, Mr. Browne continued, “During highly tense circumstances involving crowds, he put himself, others, and the police at risk.”

Although a megaphone still hangs near the entrance to his apartment in Far Rockaway, Queens, Mr. Blank said in an interview that his days of street-corner punditry are over. He expressed concern that future arrests would interfere with his academic studies.

“In that way, they’ve already silenced him,” his brother, Jason Blank, said.