(Updates with demonstrations remaining mostly orderly, calm after dark)
By Scott Malone and Ellen Wulfhorst
FERGUSON, Mo., Aug 19 (Reuters) - Police in Ferguson, Missouri, braced for another night of racially charged unrest on Tuesday as the governor and U.S. attorney general renewed appeals for calm 10 days after the fatal shooting of black teenager Michael Brown.
Street protests in the predominantly African-American community of 21,000 people have been punctuated by looting, vandalism and clashes between demonstrators and police every night since the unarmed, 18-year-old Brown was killed by a white police officer.
In the hours after darkness fell Tuesday, protesters were notably fewer in number and more subdued than on previous nights, with more onlookers milling about the fringes as civic leaders, members of the clergy and even Missouri Attorney General Chris Koster mingled with demonstrators.
Two dozen police in military-style uniforms took positions across the street from a burned-out gas station where protesters on Monday threw at least one gasoline bomb.
But confrontations between police and protesters seemed mostly isolated. A group of people playing music and dancing on top of a white truck bearing the slogan "Don't loot don't shoot" were ordered by police to move on.
Earlier in the day, St. Louis metropolitan police said they shot and killed a 23-year-old black man who brandished a knife at officers and yelled at them to "shoot me now, kill me." Two officers opened fire after he refused repeated orders to drop his weapon, police said. The incident occurred a few miles from the scene of the protests.
While apparently unrelated to the Brown killing or protests surrounding it, the shooting sparked concerns about an escalation of public anger over what many perceive as a pattern of excessive police force against minorities.
Tuesday's shooting drew scores of angry protesters who lingered well past dark outside the convenience store where the man with the knife had snatched some drinks and snacks before he was confronted by police. Police remained in a show of force to keep a lid on any potential trouble there.
GRAND JURY REVIEW COMMENCES
The aftermath of the Brown shooting was due to take a new turn on Wednesday, when the St. Louis County prosecutor's office said it expected to begin presenting evidence to a grand jury investigating the case.
In an appeal for public conciliation and calm on Tuesday, Governor Jay Nixon promised a "vigorous prosecution" of the case and "justice for the family of Michael Brown."
U.S. Attorney General Eric Holder, who planned a visit to Ferguson on Wednesday to be briefed on a separate civil rights investigation he ordered into the Brown shooting, likewise called for demonstrators to remain law-abiding in an opinion piece published online by the St. Louis Post-Dispatch.
The officer involved in Brown's shooting, Darren Wilson, has been placed on administrative leave and went into hiding as Brown's family and supporters called for his arrest.
Accounts of Brown's slaying differ. According to police, Wilson reported that Brown reached into the policeman's cruiser when Wilson approached him on the street, then grabbed for the officer's gun.
A companion of Brown said the teenager was initially shot after the officer tried to grab him through the car window and again after Brown staggered back with his hands in the air.
An independent autopsy arranged by Brown's family found he had been shot six times, including twice in the head.
SHARP WORDS FROM THE U.N.
The turmoil in Ferguson, while generating international headlines, has exposed simmering racial tensions in a mostly black town whose police force, political leadership and public education administration are dominated by whites.
It also has reignited a national debate over racial disparities in the U.S. criminal justice system, even drawing sharp words from the United Nations' top human rights envoy, Navi Pillay, a native South African.
"I condemn the excessive force by the police and call for the right of protest to be respected," she said in Geneva.
At least 57 people were arrested in Ferguson on Monday night and early Tuesday, most accused of disobeying police orders to disperse, during hours of clashes marked by volleys of tear gas fired at demonstrators and rocks, bottles and gasoline bombs hurled at police.
State Highway Patrol Captain Ron Johnson, placed in command of security in Ferguson last week after local police tactics that were criticized as overly harsh, said officers had come under "heavy gunfire" on Monday night but did not return it.
The governor and some civic leaders have suggested that the most of the trouble was generated by thugs or outside agitators bent on goading police into action. Many people heeded city officials' appeal for citizens to stay off the streets after sunset on Tuesday.
"Our innocent people need for a moment to go into their homes and not allow this criminal element to hide behind them," Johnson said Tuesday evening.
National Guard troops ordered by Nixon to assist with security in town have mostly kept their distance from demonstrators, and a mandatory curfew imposed days earlier to little effect was lifted on Monday.
Emotions could run high again next Monday, when a funeral service for Brown is scheduled.
Wilson has yet to make a public statement, but investigators said he had been cooperative in interviews with detectives.
Support for the officer was growing in the form of fundraisers and street demonstrations. A Facebook page titled "I SUPPORT OFFICER WILSON," which describes itself as a voice for law enforcement, said Wilson acted in self-defense. A separate Facebook page was offering T-shirts for sale with proceeds to go to Wilson and his family.
For full coverage (Additional reporting by Lucas Jackson in Ferguson, Carey Gillam in Kansas City, Mo., Eric Beech in Washington and Curtis Skinner in New York; Writing by Carey Gillam and Steve Gorman; Editing by Lisa Von Ahn, Peter Cooney and Jeremy Laurence)