OS ANGELES - Downtown took on the feel of a militarized zone yesterday, with hundreds of helmeted police officers jogging from block to block to keep peaceful protesters in check.
The crackdown was evident on every street corner after Monday night's melee, which protesters called a police riot and which police, who swept through the crowd on horseback, insisted was a measured response to a handful of bottle-throwing troublemakers.
Nearly 200 officers stood sentry yesterday outside the Ronald Reagan Federal Building, where a parade of women met up with a parade of teachers and students at noon. Hundreds more blocked intersections, shouting ''get back now'' at passersby who attempted to cross public streets.
''What is frustrating to me is that a whole generation of young people is growing up knowing that if they take to the streets, they have to face down tear gas, rubber bullets, batons, and pepper spray,'' said Han Shan, program director of the Berkeley-based Ruckus Society, which held a training camp before the convention to teach nonviolent protest tactics. ''It's unconscionable. We're wholly uninterested in confrontations with police.''
As he monitored his officers' movements yesterday, Deputy Police Chief Maurice Moore, said: ''We will have peace in the city. We have a lot of resources, and we're going to use them all.''
The massive show of force was exceptional even for a city plainly intent on using the Democratic National Convention to showcase its rebound from a recession, riots, an earthquake and, most recently, the widest-spread police scandal in Los Angeles history. It followed what began as an isolated incident Monday evening during a free concert by the group Rage Against the Machine but turned into 30 minutes of scattered fear and fury as the mostly peaceful crowd tried to disperse as ordered.
Instead, thousands of concertgoers who had not been tossing bottles and debris over a fence at police found themselves cornered and fired upon with pepper spray, rubber bullets, and other anti-riot ordnance. Six people were arrested, police said, one for assaulting an officer with a deadly weapon, the others for failure to disperse.
There was no official tally of injuries, although demonstration leaders said they had reports of dozens, although none serious.
In the aftermath, with each side blaming the other, the Los Angeles chapter of the American Civil Liberties Union called the police response unjustified and warned the city it should not be repeated. ''If the police were trying to incite a riot, they couldn't have done a more effective job,'' said Dan Tokaji, an ACLU staff attorney. ''These peaceful demonstrations will not be stopped by the unlawfulness of police.''
Tokaji also said police stormed into Patriotic Hall, where a Shadow Convention is being held, saying that a bomb threat had been called in and halting a live broadcast by a social justice journalism group. No bomb was found. The ACLU is considering seeking an injuction that would bar police from entering the hall.
Police officials defended their actions as necessary to prevent property damage and more-serious outbreaks of violence. During the convention, 2,000 officers are assigned to the area surrounding the hall and the entire 9,300-member force is on duty in 12-hour shifts.
''We're not going to do anything unless people are breaking the law,'' said Sergeant John Pasquariello, a police spokesman. ''If people are intimidated, I'm sorry that they are.''
Demonstrators who gathered at downtown's Pershing Square yesterday morning to call for fair wages and dignity for women, as well as those who massed at Belmont High School to rally for better education, said they refused to be cowed into quiet. All but a few condemned the trouble caused by a handful of black-clad youths, saying that their worst fear was that the issues they hoped to highlight - from corporate money's influence on government policies to the destruction of natural habitats - would be obscured by the violence.
''I don't think it's going to scare demonstrators off; if anything, I've heard people say that it makes them want to come out and be heard,'' said Steven Leigh, 51, a Seattle office worker who was at the morning demonstration. ''I think what the police did is disgusting. It's like they were just waiting for a chance to go after people.''
During the concert, police officers and youths who identify themselves as anarchists faced off through a fence, with one side hurling bottles and the other responding, after a time, with pepper spray. Yesterday, one 23-year-old anarchist who said he was at the fence said his intention was ''to stand up for peace, equality, and freedom by raising our voices and our fists.''
At 8 p.m., a police commander took to the makeshift stage to announce that the protesters and fans had 15 minutes to leave the ''protest pit'' across the street from the Staples Center. The band's permit to perform did not expire for another hour, and with fences and concrete barricades blocking three sides, they could not escape fast enough. As they tried to depart, volunteer demonstrators wearing armbands made of yellow police tape held hands in a human chain intended to help keep order.
''I was running for my life,'' said Garrick Ruiz, an activist with the Rise Up/Direct Action Network in Los Angeles. ''I was caught in the panic, trying to get over the concrete barricade. If people are dispersing, let them disperse. Why shoot them in the back'' with rubber bullets and foam projectiles known as skip rounds.
Although the peace was holding as sundown neared yesterday, police and demonstrators said they were wary of what might occur today. The theme of the scheduled protests: police brutality and other issues related to law enforcement.
Cindy Rodriguez of the Globe Staff contributed to this report.
