A Manhattan judge criticized the policing tactics in New York City Housing Authority developments, ruling on Tuesday that officers appeared to be routinely flouting the law by questioning people without legal justification.

The decision by acting Supreme Court Justice Analisa J. Torres barred the admission of 29 plastic bags of cocaine that the police seized last February from Jose Ventura in the lobby of the Baruch houses on the Lower East Side.

More broadly, the court action renewed a debate about the policing tactics in public housing, including the use of “stop, question and frisk” and vertical patrols. Officers use violations of Housing Authority rules — which forbid people from being in city housing projects unless they live there or are visiting someone — to justify the stops.

In her ruling, Justice Torres cited the testimony by Police Officer Jason Del Toro, who said the police could simply question anyone they encountered inside a public housing building. The judge wrote that officers had to have a legally meaningful reason for the stop, such as the site being drug prone.

“To the extent that Del Toro’s description of vertical patrols is accurate, that in public housing the police routinely engage in random, unjustified questioning — and there is evidence that they do — the practice would amount to a systematic violation” of the court decision that spells out the legal basis for stops and questioning, Justice Torres wrote.

Officer Del Toro approached Mr. Ventura during a vertical patrol simply after spotting him and without establishing a legal reason to question him, the judge wrote. In testimony at a suppression hearing, the officer never mentioned “whether the building or the area is drug prone,” the judge wrote.

After Mr. Ventura was arrested for trespassing, a second officer discovered the cocaine.

But in her ruling, Justice Torres wrote: “No matter the location, luxurious or modest, the police must have ‘some objective credible reason,’ to request information about a person’s residency. Officers conducting vertical patrols are not permitted to select individuals for questioning based on presence alone.”

A large volume of all the street stops police officers make in New York are for trespassing, according to an analysis of police data by The New York Times. Officers cited a suspicion of trespassing 369,000 times from 2003 through March 2010, or 12 percent of all stops. But in precincts with large clusters of public housing, up to 30 percent of stops were conducted on suspicion of trespassing.

Critics say the trespassing stops are largely unwarranted. Indeed, the analysis by The Times showed that trespassing stops were far more likely than most stops to result in nothing more than an inconvenient delay. Few moved beyond the questioning stage. Two percent of stops where trespassing was suspected — about 7,000 — yielded drugs or other contraband. A total of 81 trespassing stops yielded a gun.

Fundamentally, when officers stop people to question them, they are supposed to record both a reason for the stop — like the person’s having a weaponlike bulge in his pocket — and the crime that the person is suspected of having committed.

But among all trespassing stops from 2003 through March 2010, two-thirds — more than 257,000 — listed only the vague category of “other” or “furtive movements” as the reason for the stop. In a majority of those cases, the officers indicated that the stop took place in a high-crime area, which would satisfy what Justice Torres said the police needed as a minimum threshold to make a trespassing stop.

Paul J. Browne, the Police Department’s chief spokesman, said the judge’s decision was “not a setback” because it is consistent with new housing vertical patrol, procedures and training curriculum put in place this year.

Before making a trespass arrest, Mr. Browne said, officers are trained to ask a person: Do you live in the building? Are you visiting someone? Do you have business there? Based on the answers, and on follow-up questions, an officer might establish probable cause for an arrest, or might tell the person to leave or become satisfied that he or she can stay.

“Housing officers are trained that they must establish a reason to approach someone before questioning individuals in a housing development — for example, violations of Housing Authority rules and regulations,” Mr. Browne said. “Furthermore, the judge said the officer in the Ventura case did not adequately establish reasonable suspicion or properly articulate probable cause for a trespassing arrest.”

Mr. Browne said the department’s new guidelines and training grew out of meetings with tenants’ organizations and the city Housing Authority, and did not suggest that officers’ behavior in patrolling public housing prior to the new rules was faulty.

A spokeswoman for Bridget G. Brennan, the special narcotics prosecutor, said the judge’s decision was narrow and “we’re not concerned that it has any precedential value.”

But Steven Banks, attorney-in-chief at the Legal Aid Society, said that what Officer Del Toro “candidly admitted” in his testimony is a “serious daily occurrence.” He said it encapsulated what had led his agency, the NAACP Legal Defense and Education Fund, and a private law firm to file a federal lawsuit against the city.