NEW YORK (AP) — Twenty activists who converged on a police station to protest a controversial stop-and-frisk policy went on trial Monday in a case they hoped would highlight their cause but prosecutors called a simple matter of breaking the law.

The demonstrators, who include ministers, local activists and Princeton University scholar and civil rights advocate Cornel West, lined three rows of courtroom seats in one of the biggest group trials of protesters in the city in recent years. Supporters waited in line for spots.

The demonstrators were arrested on disorderly conduct charges in October outside a Harlem police station while decrying the New York Police Department’s practice of stopping, questioning and sometimes frisking people who are acting suspiciously or meet crime suspects’ descriptions, according to police.

Police say the practice has proven vital to curbing crime. Opponents say it amounts to racial profiling and unfairly targets innocent people.

“The system is breaking the spirit of too many young people,” West, a professor of African-American studies and the author of books including “Race Matters,” said outside court. “We were willing to be arrested, and we’re willing to go to jail.”

Prosecutors said the demonstrators deliberately crossed the line between legally protesting and disorderly conduct by obstructing a sidewalk and the stationhouse entrance and shrugging off repeated orders to move. Defense lawyers said the group was exercising constitutional rights and didn’t actually bar anyone from the precinct or sidewalk.

A judge on Monday ruled out another planned defense: that the protesters’ conduct was justified by their cause.

The New York Police Department conducted more than 684,000 of the street stops last year — more people than the entire population of Boston, Seattle or Denver. About 87 percent of those stopped were minorities, compared with 53 percent of New York City’s population.

Just 12 percent of the stops resulted in arrests or summonses. They also turned up more than 8,200 weapons, including 819 guns, police said.

The U.S. Supreme Court has said it’s legal for police to stop and question people based on “reasonable suspicion,” a lower standard than the “probable cause” needed for an arrest or summons.

Police video of the Oct. 21 protest shows a crowd gathered in front of the station, then officers speaking to the loudly chanting demonstrators through a bullhorn. The officers’ words are difficult to hear, but a defense lawyer said the police told the demonstrators to clear the front of the precinct and said they would be subject to arrest if they didn’t comply with orders.

A line of protesters remains in front of the stationhouse, the video shows. Officers go down the row and speak to the demonstrators as they are calmly arrested, many chanting “we won’t stop until we stop stop-and-frisk!” as they are handcuffed.

About 30 people were arrested; some have since taken offers to get their cases closed by avoiding re-arrest for six months. Two people took that offer only Monday, leaving 20 on trial.

“These 20 defendants made a conscious decision to be arrested in order to draw attention to a social issue,” Manhattan Assistant District Attorney Michelle Bayer said in an opening statement. ”.While some might commend their decision to take such measures to draw attention to an issue, there simply exists no legal defense for their conduct.”

But defense lawyers said the protesters acted respectfully, got conflicting instructions about where police wanted them to move and left room for people to pass by — space the video shows officers themselves walking in. And the protesters were there to try to stop what they saw as a grave injustice that happens an average of about 1,900 times a day citywide, the defense lawyers added.

“It wasn’t something they did just to get attention or for fun or just to make trouble,” one of the attorneys, Paul L. Mills, said in his opening. “Each of them reasonably believed that there was an immediate, emergency need for them to take this action.”

While the defense lawyers mentioned the protest’s purpose, Manhattan Criminal Court Judge Robert M. Mandelbaum said they couldn’t present it as an official defense.

Under New York law on what are known as justification defenses, a person can break the law to prevent an imminent, clearly worse harm than the illegal conduct itself. But there are limitations, including whether a reasonable, legal alternative is available.

Mandelbaum said the stop-and-frisk protesters had other options to address their concerns, including an ongoing federal lawsuit, and the situation wasn’t an emergency.

Protesters have tried justification defenses before here and elsewhere, with mixed results.

Disorderly conduct is a violation, not a crime. If convicted, the stop-and-frisk protesters could face up to 15 days in jail.

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Copyright 2012 The Associated Press.