In the seconds after the gunfire subsided and Gidone Gary Busch's slender frame crumpled to the pavement, stunned silence fell over a small stretch of Brooklyn's 16th Avenue.

Four of the six police officers who surrounded Busch on the street that summer's evening had pumped 12 shots into him, in front of dozens of men, women and children in the placid Orthodox Jewish neighborhood of Borough Park. Yes, Busch was swinging a hammer and had struck a cop, neighbors say. And yes, they say, Busch was unstable.

But, said witness Abe Jacobowits, "I didn't think they would shoot him. . . ."

The next day, Mayor Rudolph W. Giuliani defended the officers' actions. Both Giuliani and Police Commissioner Howard Safir said the officers were in immediate danger and had no time to use other methods. "As he continued to hit the sergeant with the claw hammer, the police fired 12 shots," said Safir, repeating what he said were eyewitness accounts from seven civilians.

Trouble is, those absolute statements from Safir's seven eyewitnesses haven't turned up since then. Instead, a raft of revelations from police documents, as well as neighborhood witnesses, has cast doubt on the official story. Jacobowits, for instance, said in an interview that he gave a statement to a police internal affairs official on Aug. 30, the night of the Busch shooting. But what he heard from Safir on news broadcasts the next day did not match what he saw.

This scenario--a controversial police shooting, a rush to defend and allegations of a coverup--has played out over and over in New York City under Giuliani and is at the heart of numerous probes targeting a police force that is hailed nationally for dramatic reductions in violent crime but also is feared in some quarters for practices that have brought a threat of intervention by the Justice Department.

The Busch shooting has become ground zero in the controversy here over the role of policing and whether lax discipline of errant or rogue officers has bred a culture of impunity that results in tragedy.

The question is among the most sensitive and politically volatile ones Giuliani faces, both as mayor and as a presumed candidate for a U.S. Senate seat, which Hillary Rodham Clinton is also seeking.

Giuliani's credibility rests in large part on his record of law enforcement successes as a mob-busting former prosecutor and as the mayor on whose watch homicides have dropped 65 percent and reported robberies 58 percent.

Some activists, however, say shooting victims such as Busch, 31, are examples of what citizens have to endure for Giuliani's law-and-order administration.

The high number of cases of substantiated police misconduct in which officers are not disciplined suggests that the problem has worsened under Giuliani.

But Joel Berger, a lawyer in private practice who was a litigator for the city during the mayoral administrations of Edward I. Koch, David Dinkins and Giuliani until 1996, says for years the culture of policing in the face of alleged wrongdoing has been "to circle the wagons and deny it."

Already the subject of a grand jury probe by the Brooklyn district attorney's office, Busch's death also is being reviewed by the U.S. attorney's office here as a possible criminal case, a Justice Department official said.

Those investigations come against the backdrop of a Justice Department "pattern and practices" probe to determine whether police misconduct or abuses are systemic. That probe has been underway since 1997, when at least two police officers tortured a detained man, Haitian immigrant Abner Louima, by plunging a broom handle into his rectum.

The Justice probe was expanded earlier this year when officers of the police department's "street crimes unit" fired 41 shots at Amadou Diallo, an unarmed street vendor, hitting him 19 times, because he moved abruptly while being scrutinized as a possible criminal suspect. Federal investigators are looking at what role racial profiling--using race as a basis for stopping people--played in this shooting and in policing generally.

If the city does not agree to cooperate with federal authorities and reform certain practices, federal prosecutors could sue to force reforms, a Justice Department official said. That could lead to the imposition of federal monitoring of police functions here--something Giuliani said in July he would not accept.

Though some reports have suggested that negotiations between the city and Justice have broken down, Marilyn Mode, a deputy police commissioner, said the sides are still discussing many issues. Neither she nor federal prosecutors would elaborate on the status of the talks.

In testimony in May before the U.S. Civil Rights Commission, which also is investigating the police department's practices, Safir defended his department as the target of those who would use tragedy for political gain. Compared to other big cities, such as the District, the New York Police Department is among the most restrained when it comes to using deadly force, Safir said.

"We have been characterized as badly trained, insufficiently monitored, negligent in our selection and hiring of recruits, and unwilling to tackle our problems honestly and directly," he said. "This type of rhetoric is absolutely untrue and highly damaging to the morale of the men and women who put on the uniform each day."

While it is true that activists here are ready to latch onto the latest tragic death as fodder for a cause, it is also true that survivors of the victims are genuinely angered.

Attorneys for Busch's family, including Barry Scheck and Johnnie L. Cochran Jr., who won an acquittal in the O. J. Simpson criminal murder trial, are questioning whether Safir's seven witnesses exist.

Busch's mother, Doris Boskey Busch--who learned of her son's death while watching the news that night--alleges a police coverup. "Absolutely," she said defiantly at a news conference last week. "I do think there was a coverup."

Safir has countered that the statements he made immediately after Busch's death were based on information available at the time. He and the mayor have urged critics to await the outcome of the grand jury probe.

The differences in the accounts of the Busch shooting hinge on whether Busch was hitting an officer when they fired. Safir's statement says the shots were fired as the hammer blows were in progress. But witnesses say Busch had struck an officer with the hammer, then ran past the cordon of police, backing up against a low wall. As he raised the hammer over his head as if it were a religious item, police formed a semicircle at least six feet away and opened fire. All of the witness accounts that have been described or published say no officer was being struck with the hammer when the shots were fired.

Neighbors say police knew--from a run to the neighborhood earlier that day because of Busch's behavior--that Busch was a disturbed man and should have subdued him in some other way. Police tried pepper spray, but that failed. An emergency services team arrived after Busch was down.

Busch's mother described her son as a victim of a bipolar disorder. He was a student of the Torah, had learned Hebrew and had recently completed a computer course with academic honors.

At the time of his death, his mother said, he was in "emotional crisis."

"He needed help," she said. "He did not deserve to die."