Antiwar demonstrations at the Academy Awards that began in an orderly manner Sunday with movie stars flashing the peace sign from their limousines, dissolved into sporadic confrontations between protesters and police.

After officers ordered the protesters to disperse, hundreds of people instead marched the streets of Hollywood for an hour.

By the end, 12 people had been arrested.

The evening's scene added to one of the oddest Oscar nights in history. Gone were the bleachers packed with eager fans. Instead, stars waited in long lines of stretch vehicles on Highland Avenue to pass through heavy security as protesters shouted antiwar slogans and waved signs.

Competing rallies -- antiwar and in support of the troops -- began hours before the ceremony's 5:30 p.m. start. Those gathered on both sides were largely peaceful, with many playing off their surroundings by hoisting faux movie posters ("Apocalypse No!") or using classic movie stars to make a point ("John Wayne wouldn't be out here bashing America.")

Los Angeles Police Department officials had ordered 300 additional personnel to be on hand Sunday because of the dual demands of the street protests and heightened security.

At a roll call earlier in the day, L.A. Police Chief William J. Bratton cautioned his officers to remain cool.

"Don't be provoked," Bratton said. "Too many people are watching."

As the opening of the show drew near, hundreds of antiwar protesters began moving from the position police assigned to them near Sunset Boulevard and Orange Drive to Highland Avenue where a seemingly endless line of limousines waited to drop off attendees.

Limo passengers occasionally popped out of sun roofs, snapping photos.

One woman yelled from the sidewalk: "Please use your time wisely. Please speak out for other people in the world."

As police attempted to push back the crowd, tensions boiled over. Dozens of protesters, some with bandanas over their faces, tried to run up Highland toward the Kodak Theatre but were stopped far short. In the days leading up to the Oscars, an anarchists' group had vowed to shut down the awards.

The crowd was quickly outflanked by police officers carrying batons and wearing riot gear. John Miller, head of the LAPD's Homeland Security Bureau, said later that officers had seen some protesters picking up rocks, but moved to intervene.

LAPD commanders shouted to their officers: "Push them. Push them. Move that crowd back."

Protesters yelled back: "Shame. Shame."

"The crowd we ran into for the most part was a law-abiding crowd exercising its 1st Amendment rights," said Assistant Police Chief Jim McDonnell. "There was, however, a significant number of anarchists who covered themselves in fake blood and conducted die-ins, and any time [an officer] moved toward them, they claimed a crime had been committed."

McDonnell said that at the height of the protests, there were 800 LAPD and 200 California Highway Patrol officers on duty, as well as Los Angeles County sheriff's deputies and federal agents.

At least one demonstrator was hit in the face and body by a baton, witnesses said.

"They didn't think this one guy was moving fast enough, and they struck him in the face with a baton," said Troy Pickard, 20, a Chapman University student.