A few days ago, a Polish teen-ager was stabbed through the heart following a drunken squabble. The incident took place on a trolley in broad daylight in the southwestern city of Wroclaw and the three assailants later walked away calmly.

By American standards, it may not have been a particularly sensational crime. But what has caused a good deal of comment and conern in Poland this week is that local police were prevented by a hostile crowd from investigating the murder.

Policemen who attempted to examine the body were kept away by bystanders who insisted they would only allow an ambulance to pick it up. When a police chief appeared on television to call for witnesses, the response was a large number of threatening messages and offensive phone calls.

The Wroclaw incident and others like it have underlined an increasingly worrisome problem for communist authorities already preoccupied with industrial unrest and economic chaos. Not only has the crime rate risen sharply over the last year, according to officials, but public confidence in the police has reached rock bottom.

Official spokesmen are pointing to the crime wave as a threat to public order, which, they argue, can only be cured by greater social discipline and respect for the security services. Leaders of the independent Solidarity trade union, however, maintain that the phenomenon has its roots in the general breakdown of trust between society and the authorities.

Whatever the sociological explanation, the surge in crime illustrates the complexity of Poland's present situation. Virtually every area of life has been affected by the social upheavals of the last nine months.The resulting political instability has an impact even on the underworld.

The government argument is that criminals and rowdies are exploiting social tension to step up their activities. An official statement last week reported that criminal offenses rose by 26 percent in the first four months of this year compared with the same period last year. Street robberies were up 30 percent, burglary 39 percent, and rowdyism by 10 percent. Even the number of road accidents had "increased considerably."

The official news media have devoted much more attention to attacks on the militia since a police substation at Otwock, near Warsaw, was burned down earlier this month following the beatings of two drunkards. It was the first incident of its kind since the crisis began -- and would have led to bloodshed had Solidarity leaders not pleaded with the mob for several hours while policemen were still inside the building.

Many impartial observers present at the scene, including Western correspondents, sympathized with the predicament of the police. Most of the crowd who attacked the building, a makeshift shack at a railway station, were clearly drunk. Given Poland's present mood, however, any strong police retaliation would have been classified as "a provocation."

Solidarity officials were quick to condemn the assault but pointed out that it could not be seen in isolation. Otwock is a notorious trouble spot and scene of frequent clashes between police and troublemakers. Both sides had undoubtedly used rough methods in the past.

Writing in a recent Solidarity bulletin, Zbigniew Romaszewski rebutted government arguments that frequent criticism of the police had undermined social trust: "That's absurd. One can't undermine trust in the police because trust has never existed. The militia's power is based on violence and fear . . . not on trust."

He went on to cite about 20 cases of people dying while under police interrogation. In all but one of the incidents the police concerned were acquitted. He alleged that to qualify for bonuses, police frequently beat suspects until they admitted their guilt.

If Romaszewski is right, police action in Poland has frequently taken the form of a trial of strength with society. Now the fear factor, once automatically weighted in favor of the authorities, has been diminished. This has provided criminals with a unique opportunity to settle accounts.

In a recent speech, the minister of the interior said people frequently ignored calls to report to the police, were generally uncooperative and refused to testify as witnesses. A police report, meanwhile, said that over 1,000 militiamen had been physically assaulted over the last six months.

The gradual disintegration of police authority has provided ammunition for Soviet Bloc propagandists alarmed at recent reforms here. Newspaper articles and speeches have painted a picture of growing anarchy and placed the blame on "counterrevolutionary elements" in Solidarity.

The extent of the crime wave should not, however, be exaggerated. The number of violent incidents has certainly increased, but so has the news media's freedom to report them. Once underplayed, hooliganism now attracts more attention.

Some Polish commentators have even suggested that hard-liners in the leadership have an interest in dramatizing the breakdown in law and order as a means of strengthening their own positions. And, despite, all the alarmist reports, Poland still remains remarkably peaceful for a country undergoing such profound changes.