In a city bracing for another convulsion, the waiting game looks like this: University students gather in a gym and rally for peace. Churches draw up plans for “safe spaces,” a refuge during potential chaos. Fringe groups pass out fliers advocating for various kinds of instigation if a grand jury decides not to indict a police officer who 31/2 months ago shot an unarmed teenager.

It’s that decision, which authorities have for days signaled was imminent but now seems slow to come, that has brought St. Louis into a bizarre holding pattern, with little agreement here about what will happen in the city after the grand jury resolution.

Eyes were trained on this weekend as the decisive moment for an area that has been rocked by the shooting and the weeks of unrest, some of it violent, that immediately followed. But news came Saturday that the grand jury was still deliberating.

Exactly when it will reconvene is uncertain, though it could be Monday or possibly sooner, according to people knowledgeable about the deliberations. They spoke on condition of anonymity because the grand jury operates in secret. Ed Magee, a spokesman for St. Louis County prosecutor Robert McCulloch, said his office is not confirming when the grand jury is meeting.

That means the eventual outcome will continue to loom as the area moves another day closer to the Thanksgiving holiday.

Michael Brown's mother talks to a crowd of protesters in Ferguson late on Saturday, as they prepared to take to the streets in protest ahead of a grand jury verdict on the police officer who shot Brown. (Facebook/My Natural Reality)

“People are getting anxious, and this doesn’t help that,” said Tony Rice, a frequent protester who helps coordinate the ongoing but small demonstrations outside the Ferguson Police Department. “I bought into the hype of it being this weekend, even though I knew better.”

Meanwhile, President Obama, community leaders and the father of Michael Brown, the slain 18-year-old, have all called for peace — a particular concern if the grand jury decides not to indict Darren Wilson, the officer.

Ferguson, the suburb where the killing took place, is prepared for chaos. Business owners have boarded up storefronts, and the FBI — which has about 100 agents and other personnel here, according to law enforcement officials — has warned in a bulletin that the grand jury announcement “will likely be exploited” to justify a broader range of attacks on authorities and infrastructure.

Two men tied to the New Black Panthers were indicted on illegal gun-purchasing charges. They were presented Friday.

“If Darren Wilson walks, America must be brought to a halt,” said Lou Downey, a supporter of the Revolutionary Communist Party, a group that advocates for a turbulent version of nonviolence and civil disobedience in Ferguson. “That means no business as usual. It means blocking streets and walking out of schools. It means we refuse to accept this.”

Saturday night, Lesley McSpadden, Brown’s mother, joined a group of about 60 demonstrators gathered around a memorial of stuffed animals and flowers marking the spot where his body had lain on Canfield Drive. The boisterous, chanting crowd turned subdued as McSpadden addressed them briefly in a light drizzle.

“I love you all,” she said. “It’s a long time coming, but it’s still coming ... justice. I just want you all to be careful. Don’t agitate the police, don’t let the police agitate you. I don’t want any of you to get hurt. When I go into court, I want all of you all with me.”

As Ferguson, Mo., prepares for a grand jury to announce whether Officer Darren Wilson will be charged in the shooting death of 18-year-old Michael Brown, here is a look back at the events leading up to that decision. (Gillian Brockell and Sarah Parnass/The Washington Post)

Her remarks after a prayer circle around the memorial came during a pause in a march led by the local protest group called the Lost Voices, formed after Brown’s death. At one point two St. Louis County patrol cars had to pause as the marchers crossed against a light. The group chanted curses at the police, but the squad cars continued on their way.

Whenever the decision does come, the response — whatever form it takes — will be of a different nature than the spontaneous protests that followed the Aug. 9 shooting. In this case, there has been plenty of advanced planning time. That has allowed protest leaders and police to draw up some rules of engagement that could keep a cap on tensions. But some in Ferguson note that even a modest instigation can change a calm gathering into a volatile one, as seen one night in August when one protester’s launch of a water bottle set off a round of tear gas.

Some in Ferguson say they fear the lead-up to the grand jury decision has caused tension to build all the more.

Gunshop owners report a spike in sales. Anonymous, a leaderless Internet group known to carry out cyberattacks to advance social and political causes, is one of several controversial groups that has arrived in the region. The Klu Klux Klan has distributed fliers around the city saying that protesters have “awakened a sleeping giant” and said that “threats of violence” against police and communities will not be tolerated and will be answered with “lethal force.”

Several black nationalist groups, including the New Black Panthers and the Revolutionary Communists, have had an enduring presence here since August, worrying law enforcement officials at the state and federal level.

Police officials, criticized in the aftermath of the shooting for zig-zagging strategies and the use of large tactical vehicles and tear gas, say they are now more prepared to deal with a volatile situation. Roughly 1,000 officers have been given civil disobedience training. The city and county police forces have created a special phone line and liaison for protesters.

“We’ve had since August to improve communication with the community, with protesters, so things can look different this time around,” St. Louis City Police Chief Sam Dotson said.

Meantime, protest leaders have been preparing for weeks for the grand jury decision by readying safe houses, emergency packs and signs while also scouting out new protest sites. They launched a Web site with information on where would-be protesters around the country have posted plans for actions in their cities. Once the grand jury announcement is made, protest leaders will send a blast text message to a list of 16,000 subscribers — mobilizing them into action across the country.

In Ferguson on Saturday, near the streets that saw heaviest protest action in August, most of the businesses had sealed their windows with plywood. Some planks were festooned with enlarged photos of raised hands — a symbol of the protest movement — and spray-painted with a message: “We Are Open.”

If the grand jury does not indict Wilson, “I think [the community] will feel like it’s open season on young black men,” said Rev. Tommie Pierson, pastor of Greater St. Mark Family Church. “You will see an outburst of protest. I hope that we can be more targeted and more disciplined in our protest.

“There should not be looting at all. That does not help our cause,” he said. “Disruption is more helpful than destruction.”

In a sign of how many are on edge, several squad cars in Ferguson were swarmed Saturday by young men from the neighborhood while officers were making a stop for a possible traffic incident. The men called themselves the “Copwatch,” formed in the wake of Brown’s death. The Copwatchers trained their cameras on the police, who at first bristled, then engaged the men in a conversation about the use of cameras and what kind of distance to keep when police are doing their jobs. A black sergeant took the lead in the talks.

“We need white officers to show up and be ‘Officer Friendly,’ ” Copwatch organizer David Whitt told the sergeant. “Stop sending someone black to be ‘Officer Friendly.’ We need white officers to understand who are the people in the community.”

Copwatch has distributed 210 cameras to watchers in the neighborhood, using donated funds, and has trained the citizen witnesses both how to use the technology and what their rights are when encountering police, Whitt said.

“Whatever the verdict is, we will be out there watching the cops,” Whitt said.

Even in recent days, in anticipation of the grand jury decision, protests have grown in number and intensity — most of them outside of the Ferguson Police Department. Some protesters say they are still being treated with a degree of hostility. Recently, after making arrests, the police have begun writing more descriptive police reports, as if building a case for any kind of action. In the write-up of Friday night’s protest, the county police included this section:

“One individual was wearing a trench coat, black ‘Anonymous’ T-shirt and a white ‘Anonymous’ mask. This individual utilized a bullhorn with a siren on it, yelling profanities that included that they wanted Ferguson Police Officer Wilson ‘dead.’ ”

Chico Harlan, Kimberly Kindy and Sari Horwitz contributed to this report.