(Reuters) - Hundreds of civil rights lawyers from across America are descending on Ferguson, Missouri as police and protesters prepare for a grand jury decision on whether to charge the officer who killed an unarmed black teenager in August.

The attorneys are arriving in Ferguson as talks between protest groups and police have stalled over a refusal by officials to rule out the use of riot gear, tear gas and militarized equipment if demonstrations turn violent should a grand jury decide not to indict police officer Darren Wilson, protest leaders say.

Wilson, who is white, shot and killed 18-year-old Michael Brown in a Ferguson street on August 9. The death sparked weeks of sometimes violent protests, and hundreds of arrests. The grand jury decision on whether to indict Wilson is imminent and police fear another wave of violence if he is not charged. Tensions in Ferguson and the St. Louis area are running high.

The lawyers, some from as far afield as New York and California, have responded to calls from the American Civil Liberties Union (ACLU) and protest groups in Ferguson to monitor police behavior in the wake of the grand jury decision. They will also take an aggressive legal posture, the attorneys said, filing quick fire lawsuits to fight potentially shoddy jail conditions, onerous bail bonds and civil rights abuses.

"We will be using the sword as well as the shield," said Justin Hansford, a St. Louis University law professor who is part of the legal team. "We have lawyers from Washington, New York, Los Angeles and Chicago. They won't just be observing. They will be filing lawsuits."

Prominent civil rights lawyer Vince Warren, executive director of the New York-based Center for Constitutional Rights (CCR) has been in Ferguson since Monday. Nicole Lee, an international human rights lawyer from Washington, arrived on Wednesday.

Warren said 280 lawyers and law students had answered emails and have volunteered to travel to Ferguson. The lawyers are taking instructions from the CCR, the National Lawyers Guild, the Missouri Chapter of the ACLU and the NAACP Legal defense Fund.

"We are in a crisis situation and we are here to ensure police let people voice their anger and frustration and don't crack down on protesters as hooligans," Warren said.

Diane Balogh, of the Missouri ACLU, said the organization had held a dozen training sessions with 100 legal observers in recent weeks. The ACLU is providing them with a mobile phone app allowing them to upload video of police behavior to a secure central database. Ferguson police have been wearing video devices since September.

Protest leaders have held meetings, and conference calls, with John Belmar, the St. Louis County Police chief, Captain Ron Johnson of the Missouri State Highway Patrol, and St. Louis City police chief Sam Dotson since mid-October, protest leaders and police say.

The focus of the talks has been on 19 "rules of engagement" proposed by the Don't Shoot Coalition, an umbrella group of 50 community and protest groups. The police have agreed to about a dozen of the rules, but have stayed silent on the use of tear gas and riot gear.

"The area we are most concerned about is the militarized response, and we are still waiting to hear on that," said Denise Lieberman, a lawyer and co-chair of the Don't Shoot Coalition.

Tory Russell, a founder of the protest group Hands Up United, said he had only been asked to one meeting with police officials, in late October, which he attended.

"All they wanted to know was where we are going to be after the grand jury decision," Russell said. "They didn't tell us where they were going to be. It was just a dig for information. We don't trust them at all."

The St. Louis County Police, city police, and the Missouri Highway Patrol, did not respond to requests for comment.