The Duane Reade robberies were accelerating: In January, they were happening every few days; last week, the gang of three started robbing 24-hour outlets twice a day, taking in tens of thousands of dollars.

As they ventured into Midtown early yesterday morning for what would be their final heist, the three suspects — armed with a pistol and carrying masks, police said — unwittingly crossed the perimeter of a trap set by the police department’s central robbery division.

More than 140 plainclothes police officers in teams of three were staking out all 47 of Manhattan’s 24-hour Duane Reade stores for a fourth straight day. Video feed from all of the stores was being sent to a central observation room, where detectives and Duane Reade security personnel kept watch.

At about 3:56 a.m., the suspects were spotted on camera entering a store at Second Avenue and 47th Street. One man stood as look-out while the others pulled up their hoods and rushed to the back of the store, where they forced a manager to open a safe and give them the cash, police officials said.

Two of the men, Kyaseem Andrews, 18, and William Barber, 23, of the Bronx, were apprehended as they left the store. Seeing the others caught, the third man, Jason Wine, 21, the alleged ringleader of the group, stashed his .380-caliber Hi-Point pistol in a refrigerator full of soft drinks and pulled off his jacket, allowing a fake security guard uniform to be seen. But police had observed him through the security cameras and he too was caught on his way out.

Wine has a previous arrest for a Duane Reade robbery and possession of a gun. Wine and Mr. Barber were last night charged with robbery and criminal possession of a weapon. Mr. Andrews was charged with robbery. Police suspect them of committing all 10 robberies at six Duane Reade stores in Manhattan and a McDonald’s in the Bronx since January 16, police said.

The robbery division’s surveillance net also caught, by coincidence, two groups of men in the midst of a violent drug dispute.

A team watching a Duane Reade at 89th Street and Madison Avenue spotted a black Grand Prix circling the block at about 2:20 a.m., police said. Thinking that the car could be related to the robberies, they wrote down a description and part of the license plate. Minutes after the car disappeared, they heard a bang that turned out to be a gunshot, police said.

Investigators believe the occupants of the Grand Prix fired at a man in a White Honda Civic, who was in the area to drop off marijuana. The drivers of a grey Dodge Charger and a black Toyota, allegedly in the area to back up the driver of the Honda, were also stopped and taken into custody yesterday.

Police lost track of the Grand Prix, but the commanding officer of the central robbery division, Inspector James Shea, spotted the car on the other side of Manhattan, heading north on Central Park West drive. He radioed ahead and a team set up a roadblock at 91st Street and Columbus Avenue.

In a haze of exhaust and screeching tires, the Grand Prix swung around the roadblock and struck an officer, who hit his head on the windshield and rolled off. Another officer fired three shots at the car, hitting it twice and striking one of the occupants in the buttocks, police said. An officer observed one of the Grand Prix’s windows roll down and a flash that may have been a gun firing a round, police said.

The Grand Prix drove up against traffic on Columbus Avenue before turning left on 97th Street, where the men abandoned the car. One man was caught trying to hide inside of the lobby of an apartment building at 778 Columbus Ave. The other, who had been shot, was caught running a few blocks away. He was taken to St. Luke’s Hospital, where he was in stable condition. The officer who was struck was treated for minor injuries and released.

A police dog later found a .380-caliber handgun stashed in a pile of snow. The abandoned Grand Prix had two bullet holes on the driver’s side, a stack of parking-violation summonses, and 10 bags of marijuana. Sitting on the floor was a large Duane Reade shopping bag.

The men in the Grand Prix, Gregory Nunez, 24, and Frank Brico, 24, were arrested and charged with assault of a police officer, criminal possession of a weapon, and criminal use of a firearm. The police were interviewing the three men who were driving the other cars, who weren’t identified. They had not been charged with a crime as of press time.

“Inspector Shea and his task force shut down a major citywide robbery pattern and captured a second, separate team of armed criminals in the process — all over the course of a few hours in the midst of a snow storm,” the police commissioner, Raymond Kelly, said. “It was outstanding work.”