Billowing clouds of smoke and bright flames spread across the night sky as gunfire, beatings and arson continued through a second night of a massive race riot here.

Eighteen people have died and at least 216 have been injured in an orgy of violence triggered by the acquittal Saturday of four white former policemen charged with the blugeoning of a black Miami businessman last December.

Miami Police Chief Kenneth Harms said there had been at least 51 "major building fires" and assistant metro fire chief Gene Perry said, "The losses will be in the billions, I'm sure.

"Each grocery store and warehouse is worth millions and we had many, many, many of them burn to the ground."

More than 1,000 National Guardsmen were called in to reinforce local police. Barriers were erected around the 20-square-mile predominantly black neighborhood of northwest Miami, to prevent whites from entering.

The acquittal Saturday in Tampa of the four ex-policemen in a televised trial inflamed Miami's black community, which has been protesting police brutality here for several years.

Dade County Manager Merrett Stierheim said the situation also may have been compounded by the recent flooding of Miami with Cuban and Haitian refugees who compete with black residents for jobs.

Downtown Miami was eerie and deserted today even before an 8 p.m. to 6 a.m. curfew imposed by tense county officials. Bus service was suspended. Gas stations were closed. And authorities halted the sale of liquor, guns and gasoline in small containers.

As of 5 p.m. today, 230 persons had been arrested, 200 blacks and 30 whites.

Black youths sped down the wide boulevards, shouting racial epithets and raising their fists in the sign of black power. Block after block of gutted buildings burned quietly in the twilight as looters loaded furniture, jewelry and other goods into their cars.

Shouting a one-word battle cry -- "McDuffie" -- angry blacks rampaged Saturday night in reaction to the all-white jury's verdict in the death of black motorcyclist Arthur McDuffie after a high-speed chase in Miami last December. The verdicts were rendered in Tampa, where the trial had been moved because of widespread publicity here.

A peaceful protest rally in front of Dade County's Metro Justice Building turned violent Saturday night, and police reinforcements charged in to defend the structure after the front doors were smashed in and rocks were thrown through windows.

What followed was an all-night orgy of brutality, mostly in black neighborhoods and directly primarily against whites, often at random. Officer Jim Baab of the Dade County Public Safety Department said that three of the victims were young whites dragged from the same automobile in Liberty City and beaten to death.

Baab identified them as Robert Owens, 14, Benny Higdon, 21, and Charles Barreca, 15. It appeared that two were the victims that Miami Herald staff writer Earnie Young said she saw lying motionless in a street while an automobile "deliberately drove over one of the bodies" three times. The crowd cheered and yelled," she reported.

Another of the dead listed as "white" by the county medical examiner's office was identified as Emilio Munoz, 66. His charred body was found in a burned-out car. The other dead were listed as an unidentified white male and four blacks.

Baab said that two of the blacks, Abram H. Phillips, 21, and Elijah Aaron, were killed by policemen returning fire. Another, Michael Scott, 17, was said to have been shot by a security guard while burglarizing a drug store. The fourth, Kenneth Lee China, 22, was fatally wounded in the chest as he stood in front of his house.

Hospital emergency rooms were overburdened with the injured, some of whom required surgery. One of the injured whites reportedly had been shot in the side. His tongue and one ear had been cut off, and a red rose had been stuffed in his mouth.

The violence continued through the day but no further deaths were reported. Columns of black smoke billowed from dozens of fires in Liberty City. Burned or overturned cars littered some streets. Looting added to the toll of damage, which was expected to total millions of dollars. A number of white-owned businesses were wiped out by fire or theft.

Louis Lopatin, a white, said that $10,000 in jewelry was taken from his store. "Everything is lost in here," he said. "I don't think I'm ever going to open here again."

About 350 National Guard troops set up headquarters in an armory, and 450 more were reported in route from Orlando, 220 miles north of Miami. Scores of heavily armed guardsmen were deployed to the perimeter of Liberty City, located in northwest Miami. Police said that they, too, were keeping to the perimeter and venturing into the troubled area only in response to emergencies or looting.

The National Guard was called out Saturday night by Gov. Bob Graham in response to a request from local officials.

Meanwhile, in the modest neighborhoods of one-story, brightly colored bungalows, black residents were trying to restore order. "Be cool, brothers and sisters," boomed the loudspeaker of an unmarked sound truck. "Stay at home. They're bringing more troops in tonight."

The voice on the loudspeaker belonged to Jerry Rustin, the disc jockey of soul station WEDR. "I'm trying to help the blacks get off the streets, so they won't get shot by policemen," Rustin said.

The outcome of the trial was "the straw that broke the camel's back," he said. "There have been other beatings and the police have walked away. An 11-year-old black girl was molested by a white policeman in the back of his police car and he only got six months probation. I've even had a gun put at my head."

Across the street from the sound truck, patrolman Charlie Hebding, blue-eyed, blond and badly sunburned from a day on the barricades, stood blocking the street with three helmeted National Guardsmen toting M16 rifles.

"I don't believe our police department is a brutal police department perse," he said. "We're professional. You do have isolated incidents like any other place."

On his hip a police radio crackled, reporting that a sniper down the street had just wounded two police officers, one in the abdomen.

Other attempts also were under way to calm emotions of the Dade County's black residents who make up about 15 percent of the population:

Acting U.S. Attorney Atlee Wampler announced that he would seek indictments of the four acquitted ex-policemen by a federal grand jury under U.S. civil rights law. He said he would begin to present evidence to the grand jury Wednesday.

The federal Justice Department sent a team from its community relations service to Miami to meet with community leaders in search of "lawful means of redress."

The Dade County Community Relations Board convened an emergency session today to seek solutions to the accumulated grievances of the black community. Former county commissioner Athalie Range, regarded as a moderate, told the board, "White leaders need to say that they are outraged too, and they need to come up with some solutions." If solutions are not forthcoming, she said, the violence is "going to go on and on."

Alluding to the outcome of the McDuffie case, Range said, "We realize that if we do something wrong, we've got to be punished. But we also realize that if someone does something to us, they've got to be punished too. Right now, it's a one-sided situation."

Although the McDuffie verdicts were the trigger, blacks' unhappiness with the Dade County criminal justice system has been longstanding. Blacks were jarred into protest more than a year ago when police on a drug raid broke into a house and beat one of its occupants before discovering they had the wrong address.

More recently, a Hialeah policeman fatally shot a black teen-ager and said that he caught the youth trying to burglarize a warehouse. But the youth's sister said that he had merely approached the warehouse to urinate outside.

And there was the recent conviction of Dade County School Superintendent Johnny L. Jones on a grand-theft charge related to his attempted purchase with school funds of nearly $9,000 in deluxe plumbling fixtures. It became known as the "gold plumbing caper," but to some blacks it seemed to be a racially motivated attempt to "get" the county's most respected black public official.

Thus, The McDuffie case became, in effect, the last straw.

"I think this has been smoldering for a long time," said Marvin Dunn, associate vice president of Florida International University and a moderate voice in the black community. "The McDuffie case was just the spark."

He called the violence "a purely spontaneous, unorganized reaction . . . There's no sense of organization at all. It was mob rule out there last night. It was an expression of frenzy, of frustration, and it's not finished yet, I'm afraid."

If a sampling of radio talk shows was any indication, the violence generated a sense of shock in the community at large and perhaps touched off some introspection. Robert Hall, the program director of WMBM, which has a large following in the black community told his audience, "We're turning into the savages that white America thought we were in the beginning . . . We just went back 100 years last night."

"Yes," Hall continued, "an injustice has been done in the Arthur McDuffie case, but do we rectify it with the bullet or the ballot? I say the ballot."

The Miami blacks' anger perhaps had been foreseen by Dade County Circuit Court Judge Lenore Nesbitt, who called the case a racial "time bomb" and moved it to Tampa for trial.

McDuffie, a 33-year-old insurance man, died four days after a Dec. 17 high-speed chase involving his motorcycle and a host of police cars. Prosecutors said the four policemen had fatally beaten him, in an example of "street justice handed out by a group of police officers who lost control of themselves."

Officers Alex Marrero, Ira Diggs, Michael Watts and Herbert Evans Jr., were tried on charges ranging from second-degree murder and manslaughter to aggravated battery to tampering with evidence to cover up the incident.