Robbery is up more than 30 percent in the District in 2012, a jump that has forced police to redeploy resources, shake up tactics and urge residents to provide tips and act as witnesses in investigations.

This year’s increase is much larger than the rise last year, when robberies increased 5 percent, according to department statistics.

There were 875 robberies reported in the District through March 18. Driving the increase has been a jump in incidents in which a gun was used; those crimes are up more than 70 percent.

Robbery numbers are up in every police district.

Commuters, pedestrians and shop workers have had bags snatched and registers looted; they’ve been threatened with weapons and bare-handed violence; and robbers, alone or in groups, have grabbed cash, tech gear and handbags.

The rise is significantly steeper than that seen in some other big cities. Robberies were up about 8 percent in New York through March 11, according to police data, and rose about 10 percent in Philadelphia during the same time.

The increase in the District comes as some other measures of violent crime, including homicide, are falling.

The spike is “on the top of everyone’s mind,” D.C. Council member Muriel Bowser (D-Ward 4) said. Residents “are becoming a little bit more vigilant and aware of their surroundings,” council member Yvette M. Alexander (D-Ward 7) said.

It’s meant busy days and nights for city police. “We are hammering robberies,” Police Chief Cathy L. Lanier said in an interview. “We are putting everything we have into this.”

Robbers look for opportunities and see them in people carrying expensive electronics and other items that are easily resold, Lanier said. East of the Anacostia River, she said, they also target such fashion items as Nike sneakers and Helly Hansen jackets.

Increasingly, police strategies are targeting robbers and thieves. Uniformed patrols have increased; plainclothes officers have staked out unlocked “bait cars”; Metro police have set up decoy teams in which a plainclothes officer poses as a sleeping commuter with visible cash or electronics, then others swoop in to make arrests after the goods are purloined.

Lanier hopes word of the traps will spread, news of “deterrence arrests” will dissuade potential robbers, and the community will turn against criminals and collect rewards in exchange for useful tips.

Police also are targeting the market for stolen goods: They recently announced a lengthy operation that targeted businesses authorities said sold “hot” property, making 16 arrests and seizing hundreds of cellphones, iPads and other devices.

“There are so many places in the city that will resell these items,” Lanier said. “There’s no shortage.”

Authorities also are exploring technological solutions. Lanier and other big-city police leaders have asked regulators and wireless-network operators to allow the remote shutdown of stolen cellphones, which would lower their resale value.

“Generally, I would say that the police response has been incredible,” Bowser said. “They’ve kind of thrown everything at it.”

Police also welcome the help of witnesses, who can help make prompt arrests. According to Police Lt. William G. Fitzgerald, a bystander’s view of events is broader and less traumatic than a victim’s, making the witness’s report particularly valuable. “Witnesses see the whole picture,” said Fitzgerald.

Lanier says police have made more than 200 more robbery arrests this year than at this point in 2011. That’s an increase of 107 percent, she said.

Alexander says she has noticed the effects of the department’s efforts. “It has quieted down,” she said. “Maybe they are patrolling a little bit more. Or the criminals know when an area is hot and people are paying attention.”

Still, police continue to investigate many unsolved cases, since victims cannot always provide useful information and leads can be scarce.

Citing “community concerns,” D.C. police now regularly report robbery-related arrests in news releases. And they have increasingly turned to Twitter and other electronic methods to spread information about crimes in the city almost as they happen.

To observe the aftermath of the crimes, a Washington Post reporter visited several scenes of robberies tweeted by police, interviewed victims, bystanders and witnesses, and read incident reports.

The variety of incidents illustrates the reach of robbery, a crime to which almost anyone could fall victim. Four young men took a man’s book bag and laptop after flashing a handgun on Alabama Avenue SE, according to police reports; someone snatched the bag of a woman walking in the Petworth area; a man laughed as he ran off with a 26-year-old woman’s iPhone near Union Station; a man showed a pistol in a Southeast McDonald’s restaurant and made off with cash.

In one late February incident, the victim was a woman returning from a visit with her daughter; the take was the woman’s vehicle.

Twitter, Feb. 22
. . . Robbery Hold up Gun in the 3500 blk of A st, SE...”

Thirty minutes after she was robbed, a woman stood shaken but physically unharmed amid six police officers in the darkness of a warm Washington night.

“They stuck a gun in my face,” she said, crying as she recounted the attack to a reporter on a street lined with low-slung apartment buildings. “I just knew they were going to shoot me.”

They did not — but they did drive off in her Toyota, launching a police search for three people she said cornered her at about 9 p.m. as she returned home.

Twitter, Jan. 27
. . . Robbery // 900 M Street, NW . . .

Two blocks from the Walter E. Washington Convention Center, police officers sat on couches in the glass-plated lobby of a high-rise apartment building as they spoke with a 24-year-old man who said he was robbed of $800 in cash sometime before midnight. The interview was halting: The victim was not a native English speaker, and he appeared to be intoxicated.

The man said nine young men approached him, and one showed a gun, according to a police report. The man said he handed over a wallet and then ran into the apartment building, where a guard called police.

Several uniformed officers and a detective came to investigate. Their presence caused a stir in the lobby. Nadim Bacho, 31, watched the scene intently as he left the building; last year, he said, his cellphone was snatched as he walked off the Metro in Foggy Bottom, but he ran the offender down.

“Things like this happen,” Bacho said. “It could happen anywhere in the city.”

Twitter, Jan. 21
“Robbery Gun of an Establishment _1847 hours _7300 block of Georgia Ave NW . . .

A man walked through the front door of the Mayfair Liquor store in Shepherd Park on a chilly Saturday evening and asked for a cold bottle of Ciroc vodka. Then he produced a shotgun, two store employees told police.

He pointed it at one of the workers, according to a police report, and the worker dropped to the ground. “Don’t do anything,” his co-worker said. Then the gun turned toward him, the police report said, and the employee saw brown eyes through a black ski mask.

“Put all the money in the bag,” said the robber, according to the report. As the employees filled a black grocery bag, the gunman said he wanted money from a safe. “I’m not playing,” he told them.

The workers convinced him there was no safe, according to the report, and he fled down an alley.

Police remained along Georgia Avenue for more than an hour after the robbery. Detectives interviewed an employee; evidence technicians snapped photographs and looked for surveillance video. Outside, officers with dogs searched for the gunman.

Police lights bounded off storefronts — a law firm, construction contractor’s office, a security firm.

At the end of the block, Mersha Abate’s Geranium Market was open but empty.

Abate said he was not worried about being targeted himself. “It’s not good news, but this is unusual,” he said. “This is a high-class neighborhood.”

Still, he was unsettled. “These times are bad because of the economy,” said Abate, who opened his market 10 years ago. “The economy makes the difference. I don’t know what to say.”

Police made an arrest in the robbery four days later, but the community remains on edge.

Reporter Mike DeBonis contributed to this report.