For the second night in a row, isolated incidences of violence between blacks and police unnerved this racially edgy city.

While temperatures and tensions had cooled during an afternoon thundershower, nightfall brought renewals of the vandalism that began Tuesday with the shooting of a Dade County police officer. But officials were confident the latest confrontations have neither the motivation nor community support of the rioting which took 18 lives here in May.

Police by 1 a.m. had received reports of two more shootings but had no details other than the fact that civilians, not police, were involved and that neither caused a fatality. However, in periodic sweeps down area streets, patrol teams were fired on by snipers, without effect, police said.

The police blockades which were used to cordon off a large area of the Liberty City ghetto Tuesday night had come down at 7 this morning and except for the closing of summer sessions of public schools, it had been business as usual during the daylight hours on Miami's north side.

But after two incidents in which people were injured, as well as sporadic gunfire occurring after 9 tonight, police reestablished barricades on the busiest streets of Liberty City "to stop casual traffic and sight-seers," Police Commander Joe Keefe said.

Among the incidents reported by 10 tonight were the injury of a female officer when an auto part was hurled through the window of her patrol car and minor injuries to several passengers and the driver of a city bus that was stoned.

All but two of the people injured Tuesday night were released shortly after being treated at hospitals in the Liberty City area on the north side of Miami. Only two shooting victims, a plainclothes policeman and a 15-year-old boy, both of whom were shot in the back, remain hospitalized.

Eleven persons, nearly all young black males, were arrested on various minor charges, such as vandalism, burglary and disorderly conduct.

Nearly all of the trouble Tuesday occurred just beyond the Miami city limits in Dade County. Miami police, whose involvement was limited to manning blockades, reported no disturbance-related injuries or arrests.

Maj. Frank Clifton, who was directing the county police command center in Liberty City, attributed the short-life of the disturbance to a quick and massive response by his department, which was criticized during the May rioting for reacting slowly and permitting the disturbances to spread.

"What occurred last night cannot be covered under the umbrella of the McDuffie incident," said County Manager Merrett Stierheim. He was referring to the beating death of black insurance man Arthur McDuffie and the subsequent acquittal of four white Metro police officers charged with his murder which triggered the May rioting.

"Last night was lawlessness, period. Criminal activity that cannot be tolerated," Stierheim said.

Reminders of the rioting 60 days ago remain along the wide, palm-lined boulevards of Liberty City. Firebombed buildings remain charred and unrepaired.

There was no looting Tuesday night and little arson. One service station was torched, some said because its black owner had the highest prices in town -- about 30 cents a gallon higher than a nearby station.

Some of the whites who either ignored police barricades or were trapped in the area when the trouble began had their cars pelted with rocks and bottles, accounting for most of the injuries.

The disturbance began Tuesday about 3:30 p.m. when Metro Sgt. Fred Pelny was shot while trying to stop an apparent holdup.

Pelny was part of a new police robbery supression team, on its first mission in Liberty City. The team, composed of plainclothes officers on foot and in unmarked vehicles, was put together in response to an outbreak of robberies in the James E. Scott public housing project, an aging rundown symbol of the urban blight that is Liberty City.

Pelny and two other white officers were in a van when they saw three young blacks attempting to rob a white motorist who had stopped for a traffic light at one of the major intersections in Liberty City. Each of the officers grabbed one of the suspects; as they struggled with the youths, a crowd gathered.

During the struggle, the officers and suspects fell to the ground and a shot was fired. In the confusion that followed, the suspects fled into the cheering crowd.

Police said a number of shots were fired from the crowd, and some officers speculated that the weapons were among the more than 1,000 guns stolen in the looting that accompanied the May rioting.

Pelny was shot in the back but the bullet hit high and struck no vital organs. He was in good condition today at a Miami hospital. Police said Pelny's service revolver had been fired, but when was unclear.

Meanwhile, the motorist victim sped away from the scene. Several hours after the incident, a 17-year-old surrendered at the local police station, saying he had been one of the participants in the robbery. But because the motorist has not come forward to file a complaint, police said they had a victimless crime and were forced to release the suspect.

In addition to Pelny, 35, the injured police were Sgt. Rodney Wilson and officers William Kinnebrew, John Butchko and Jack Buckley.

The last three officers were injured about 9 p.m. when a single shotgun blast shattered the rear window of their patrol car. Buckley was shot in the upper back and Kinnebrew and Butchko were hit by flying glass.

About 20 minutes later, Watson, 34, was struck in the right shoulder by a bullet that came through the rear window of his cruiser.

All three shooting incidents involving police occurred on busy 22nd Avenue, the main thoroughfare of Liberty City.

"Part of the problem is that maybe we shouldn't have sent white cops in there," said Officer Henry Weatherspoon, one of the 108 blacks on the metro police force of 1,458.