*Police department officials appeared unprepared for the size and unruliness of the crowd, which included supervisors as well as rank-and-file members. There were relatively few police barricades up and they were sparsely attended by uniformed officers who joined in the chants, raised their own fists in support or passively stood to one side. Almost no effort was made by the 300 officers on duty to keep protesters from breaking police barricades to rush the steps of City Hall. Alarmed officials inside City Hall, fearing that the building would be overrun, bolted the doors and summoned a half-dozen uniformed guards from the basement to act as a last line of defense.

*Officials with the Patrolmen's Benevolent Association, which organized and promoted the rally, appeared unable to control their members. Though they had assured police officials that the demonstration would be peaceful and that there would be at least 150 members acting as marshals, neither the marshals nor the union's leaders inhibited the protesters' movements. Nor did they appear to discourage protesters from displaying obscene and inflamatory signs, like those depicting the Mayor with a large Afro-style haircut and swollen lips or another making reference to Mr. Dinkins as a "washroom attendant." In the words of Suzanne Trazoff, the deputy commissioner, "Nobody was in control." Washington Heights Seemed Final Straw

The roots beneath the disturbance were deep. Protesters condemned the Mayor for his refusal to approve the issuance of semiautomatic pistols, saying officers had less firepower than criminals. They took issue with the appointment of a Mayoral commission to investigate charges of police corruption. They complained, too, about the Mayor's support of the formation of an all-civilian review board to investigate police misconduct.

But the final straw, many said, was Mayor Dinkins's handling of last summer's Washington Heights unrest and what they perceived as his sympathy for and support of the family of Jose (Kiko) Garcia, a Dominican immigrant with a drug conviction who was slain July 3 in a confrontation with a police officer. Many officers at the rally said they were particularly incensed that the victim's family had been invited to Gracie Mansion. The officer, Michael O'Keefe, was exonerated by a grand jury earlier this month.

The culmination of those simmering complaints came the morning of September 16.

Police officials had prepared for the rally for at least a month. But there was no special meeting between the Patrolmen's Benevolent Association and department officials just before it began. There seemed no need. P.B.A. officials had promised a peaceful march with no alcohol. "The demonstration was described to us so carefully," said Ms. Trazoff, "there was no reason to think it would really require handling."

At the start, at least, that reasoning held. Police officers who arrived at City Hall in buses the morning of the rally began the march as planned. They walked twice around the agreed route, circling City Hall. By 10:50, however, two demonstrators climbed atop buses, held aloft a huge sign and used an obscenity to describe the all-civilian review board. They were cheered and applauded by the crowd. At that moment the mood shifted.

"Take the hall! Take the hall!" protesters shouted. In a moment, the first demonstrators started clambering over the blue police sawhorses east of City Hall. Cheering, screaming and running, hundreds and finally thousands then swarmed the steps. 'Dunk the Dink' And Much Worse