CHICAGO — Demonstrators prepared Monday to launch another day of major protests in Chicago as world leaders met at the NATO summit, while commuters heading into the city found themselves navigating extra security and revised train and bus routes designed to dodge the summit zone.

Many downtown businesses told their employees to stay home during the second and final day of the summit — where world leaders are discussing the war in Afghanistan, European missile defense and other security issues — because of traffic snarls and the possibility of more protests.

The weekend's protests drew thousands and called attention to everything from foreign policy to the economy, but were mainly peaceful. The biggest conflict came late Sunday, when a group of protesters clashed with police at the end of a march.

On Monday, a group of demonstrators with the Occupy Chicago movement were planning to protest outside of Boeing Corp.'s headquarters. Officers were stationed there already Monday morning, and an orange barricade blocked off the building's entrances. Occupy claims the multi-billion-dollar aerospace company avoids paying taxes because it produces airplanes for the U.S. military.

More than two dozen Metra rail stations along a line that carries around 14,000 riders in from the southern suburbs on most weekdays were closed and stations and platforms were being patrolled by a larger contingent of law enforcement personnel and K-9 units. The Chicago Transit Authority was rerouting 24 buses through the summit zone.

But commuters who did brave their daily trip were finding something they were unaccustomed to: a seat on the train or bus. Early trains had plenty of room to stretch out, a sign workers were heeding warnings to stay home. Those who did commute were prohibited from bringing food or liquids — including coffee — and could only carry one bag.

"The no food or beverages — that's the only inconvenience," said Pete Dimaggio, 55, a credit manager. "Now I have to buy my lunch. They are making me spend money."

Monday's protests were expected to be far smaller than the weekend's events.

Andy Thayer, one of the main protest organizers, said he expected many demonstrators from out of town to leave Sunday night. After the Boeing demonstration, immigration rights activists were planning to travel to the small village of Crete, about 35 miles south of Chicago, where federal officials are considering building a nearly 800-bed detention facility for illegal immigrants slated for deportation.

Thayer said he still expected a strong contingent of protesters to show up for the Boeing protest and decried how city leaders and police officials have handled the protests.

"I am disgusted, particularly, with the upper echelon of our city," Thayer said.

On Sunday, several thousand protesters marched through downtown Chicago in one of the largest demonstrations the city has experienced in years, airing grievances about war, climate change, economic inequality and a range of other complaints.

But the diversity of opinions also sowed doubts about whether there were too many messages to be effective.

Some of the most enduring images of that protest were from a clash between a small group of demonstrators and a thick line of police who tried to keep them from the lakeside convention center where President Barack Obama is hosting the NATO summit.

The protesters tried to move east toward the venue at McCormick Place with some hurling sticks and bottles at police. Officers responded by swinging their batons. The two sides were locked in a standoff for two hours, with police blocking the protesters' path and the crowd refusing to leave.

Police Superintendent Garry McCarthy said 45 of those protesters were arrested. Police said four officers were hurt, including one who was stabbed in the leg. Some protesters had blood streaming down their faces.

Hundreds of protesters gathered late Sunday night near the Art Institute of Chicago as first lady Michelle Obama hosted a dinner for spouses of NATO leaders inside. At least 100 Chicago police officers in riot gear were also at the scene.

The protests, including relatively smaller demonstrations on Friday and Saturday, lacked the size and single message that shaped the last major protest moment in Chicago in 2006, when nearly half a million people filled the city's downtown to protest making it a felony to be an illegal immigrant.

Associated Press writers Don Babwin, Ryan J. Foley, Carla K. Johnson, Robert Ray, Jim Suhr, Nomaan Merchant and Michael Tarm contributed to this report.