The intervention, ordered by Missouri Gov. Jay Nixon, came as President Barack Obama spoke publicly for the first time about Saturday's fatal shooting of Michael Brown and the subsequent violence that shocked the nation and threatened to tear apart Ferguson, a town that is nearly 70 percent black patrolled by a nearly all-white police force.
Obama said there was "no excuse" for violence either against the police or by officers against peaceful protesters.
Nixon's promise to ease the deep racial tensions was swiftly put to the test as demonstrators gathered again Thursday evening in the neighborhood where looters smashed and burned businesses on Sunday and police repeatedly fired tear gas and smoke bombs.
But the latest protests were a world apart from the earlier demonstrations, with a light, even festive atmosphere and no hint of violence. The streets were filled with music, free food and even laughter.
Protester Cleo Willis said the change was palpable.
"You can feel it. You can see it," he said. "Now it's up to us to ride that feeling."
After a particularly violent Wednesday night, Nixon said local police would no longer be in charge of the area, although they would still be present. He said Highway Patrol Capt. Ron Johnson, who is black, would be in command.
The change was meant to ensure "that we allow peaceful and appropriate protests, that we use force only when necessary, that we step back a little bit and let some of the energy be felt in this region appropriately," Nixon said.
"Ferguson will not be defined as a community that was torn apart by violence but will be known as a community that pulled together to overcome it," the governor said at a news conference in the nearby community of Normandy.
The governor was joined at a news conference by the white mayor of St. Louis and the region's four state representatives and the county executive, all of whom are black.
Johnson said he grew up in the area and "it means a lot to me personally that we break this cycle of violence." He said he planned to keep heavily armored vehicles away from the scene and told his officers not to bring their gas masks.
By late afternoon, Johnson was walking down the street with a large group of protesters as they chanted "Hands up, don't shoot," a reference to witness accounts that described Brown as having his hands in the air when the officer kept firing. He planned to talk to the demonstrators throughout the night.
"We're going to have some conversations with them and get an understanding of what's going on."
At one point, Johnson spoke to several young men wearing red bandanas around their necks and faces. After the discussion, one of the men reached out and embraced him.
At the burned-out QuikTrip near the shooting scene, children drew on the ground with chalk and people left messages about Brown.
Earlier Thursday, Obama appealed for "peace and calm" on the streets.
"I know emotions are raw right now in Ferguson, and there are certainly passionate differences about what has happened," Obama said, speaking from the Massachusetts island where he's on a two-week vacation. "But let's remember that we're all part of one American family. We are united in common values, and that includes the belief in equality under the law, respect for public order and the right to peaceful public protests."
Residents in Ferguson have complained about the police response that began soon after Brown's shooting with the use of dogs for crowd control — a tactic that for some evoked civil-rights protests from a half-century ago. The county police took over, leading both the investigation of Brown's shooting and the subsequent attempts to keep the peace at the request of the smaller city.
County Police Chief Jon Belmar said his officers have responded with "an incredible amount of restraint" as they've had rocks and bottles thrown at them, been shot at and had two dozen patrol vehicles destroyed.
The city and county are also under criticism for refusing to release the name of the officer who shot Brown, citing threats against that officer and others.
The hacker group Anonymous on Thursday released a name purported to be that of the officer, but the Ferguson police chief said later that the name was incorrect.
Like last year's Trayvon Martin shooting, social media brought international attention to a tragedy that might otherwise have been known only to the immediate community. Ferguson spawned a proliferation of hashtags and was the dominant subject Thursday on Twitter, Facebook and other sites. Journalists and protesters offered real-time pictures, videos and text reports, and the world responded, often in outrage.
Police have said Brown was shot after an officer encountered him and another man on the street. They say one of the men pushed the officer into his squad car, then physically assaulted him in the vehicle and struggled with the officer over the officer's weapon. At least one shot was fired inside the car. The struggle then spilled onto the street, where Brown was shot multiple times.
The officer involved was injured, with one side of his face swollen, Ferguson Police Chief Thomas Jackson said.
Dorian Johnson, who says he was with Brown when the shooting happened, has told a much different story. He has told reporters that the officer ordered them out of the street, then grabbed his friend's neck and tried to pull him into the car before brandishing his weapon and firing. He says Brown started to run and the officer pursued him, firing multiple times.
Attorney General Eric Holder has said federal investigators have interviewed eyewitnesses to the shooting. A person familiar with the matter, who spoke on condition of anonymity because the investigation is ongoing, said federal authorities have interviewed Johnson.
Holder spoke by telephone Thursday with Brown's family to offer condolences and to tell them that the Justice Department was committed to a full and independent investigation.
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Associated Press writers Alan Scher Zagier and Jim Suhr in Ferguson, Eric Tucker in Washington and Hillel Italie in New York, and AP researcher Rhonda Shafner, also in New York, contributed to this report.