In Wisconsin, a group of environmentalists plans to bicycle to Chicago's G-8 and NATO summits to protest an economy that relies too heavily on fossil fuel.
In California, a nurses union has a permit for a Chicago march the day before the summits to highlight economic inequalities and a lack of health care for too many Americans.
Chicago Police Department estimate of 2,000 to 10,000 demonstrators to the national Occupy movement's call for 50,000.
"It's obviously the $64,000 question — I've seen estimates of thousands of protesters and tens of thousands. No one really has any idea," said Jeffrey Cramer, head of the Chicago office of Kroll, a corporate security firm doing work related to the summits.
That leaves city officials, Chicago police, federal agencies and security experts who advise corporations all trying to figure out who will show up and whether anybody will be looking to cause trouble.
A reminder of the stakes came Thursday in federal court, where city lawyers agreed to pay $6.2 million to about 800 people detained by police in what a judge called unjustified mass arrests that ended a 2003 Iraq War protest downtown.
Mayor Rahm Emanuel and event organizers are playing down the potential for violent protest and focusing on the chance to showcase Chicago as an international tourism and business center. The rare back-to-back meetings of the Group of Eight industrialized nations and the NATO gathering of key U.S. military allies in one city will bring worldwide attention.
At the same time, authorities are drawing up contingency plans for possibilities that range from downtown streets choked with demonstrators to elusive bands of anarchists who could show up to tangle with police.
"It's apprehension of the unknown," Cramer said.
Many protest group leaders say they are committed to causing no harm, but they acknowledge they are likely to see multiple sources of conflict with police while they're here. From anonymous provocations of violence on the Internet to troublemakers mixed in with the protesters, when anxious cops and simple breakdowns in crowd control mix, a lot could go wrong.
One of the 2003 anti-war protesters in line for the city settlement, Cheryl Angelaccio, 49, of Morton Grove, said she hopes police will show more restraint when she demonstrates at the overlapping G-8 and NATO gatherings.
"These are peaceful protests. And unless there is a need to respond in that fashion, OK, but I have not been at a protest when that has been needed," she said. She added she was encouraged by how Chicago police gave demonstrators an option of leaving or being arrested at a more orderly Occupy protest last fall.
Thistle Pettersen, a leader of Grassroutes Caravan, is planning to bring a group of 50 bike riders to Chicago to protest for a clean environment. The Chicago summits are getting a lot of buzz in politically active circles around the country and Pettersen said she expects big crowds.
"I've heard a lot of real, legitimate interest," said Pettersen, who lists her occupation as child care worker and folk singer.
The group has demonstrated at several political gatherings in recent years, and its members have to sign an agreement that they will not commit any acts of violence or property damage, Pettersen said. Still, she said that's no guarantee even groups like hers won't find themselves in the middle of a disturbance.
Citing the 2004 political nominating conventions in Boston and New York, she said the appearance of "agents provocateurs" who clashed with police at the end of otherwise peaceful marches may be an attempt to make mainstream demonstrators look bad.
"You've got to have your street smarts when you're out there and use your intuition," Pettersen said. "That's part of the risk of protesting in America these days."
Chuck Idelson helps organize the California Nurses Association, a union that has shown a large and steady presence in Occupy demonstrations, and said he expects that G-8 will draw the largest crowds of the year to demonstrate.
"The G-8 are, certainly, the countries that are the most prominent and, certainly, determine the direction of the largest economic powers in the world," said Idelson, whose group holds a permit for a demonstration and march on May 18, the day before the G-8 summit begins.