“We wish there was a leader in City Hall,” Mr. Lynch said.

The drop in arrests is particularly striking for low-level misdemeanors and so-called quality of life violations, like riding a bike on the sidewalk. Arrests for offenses that a few weeks ago were common — loitering, turnstile jumping, lying down on subway benches — are suddenly rare.

The number of cases handled by the arraignment courts fell 36 percent in December compared with the same month last year, and most of the drop came in the last two weeks of the month, court officials said.

Just in the last two and a half weeks, arraignments for misdemeanors have fallen about 60 percent, to 2,581, from 6,395. The drop was more pronounced for people arrested for violations, like disorderly conduct: a 91 percent decline to 97 cases, compared with 1,157 over the same period a year ago.

There have been similar declines in the past, but they have come after natural disasters and other emergencies, court administrators said. The last one occurred during Hurricane Sandy in 2012. Another slow period followed the terrorist attacks in September 2001.

Few managers in the court system expect the current downturn to last. Many public defenders, however, said they hope the steep decline in minor arrests will become permanent. They noted felonies did not rise over the last three weeks as arrests for low-level crimes plummeted.

“This proves to us is what we all knew as defenders: You can end broken-windows policing without ending public safety,” said Justine M. Luongo, the deputy attorney-in-charge of criminal practice for the Legal Aid Society.

Legal Aid lawyers and veteran clerks in the courts said the police appeared to be bringing in only people who they must have taken into custody: shoplifters caught by store owners, drunken drivers, people accused of assaulting their spouses or others accused of violent crimes. Felony arraignments did decline but not nearly as precipitously as misdemeanors, decreasing 25 percent to 1,026.