Four people were killed in the District late Thursday and early yesterday, prompting top police officials to invoke crime-emergency powers that allow them to more quickly change officers' schedules and restrict days off.

D.C. Police Chief Charles H. Ramsey has not turned to emergency powers since the summer of 2004, after a spike in juvenile auto theft. Ramsey said last night that he felt he needed more flexibility because robberies have increased recently and 24 killings have been recorded in the past 32 days.

"We have to keep the streets safe," Ramsey said. "These are the kinds of things that spread fear and panic in the community."

The four killings do not appear to be related, police officials said. The victims included a 17-year-old who was shot after he apparently refused to remove a ski mask; a 55-year-old man slain in a drug-related argument over $5; a 24-year-old transgender person killed in an apparent robbery attempt; and a 32-year-old man, police said.

The emergency powers allow commanders to adjust schedules without giving officers 14 days' notice, as required under the union contract. Ramsey said he also will restrict days off for the next 45 days and increase patrols in hard-hit neighborhoods and retail areas.

Union officials reacted angrily to Ramsey's announcement, which they learned about from a reporter. They said that officers already are exhausted from working 12-hour days and mandatory overtime shifts, and that the initiative could spoil their holiday plans.

"It's just ridiculous," said Sgt. Gregory I. Greene, chairman of the D.C. police labor committee for the Fraternal Order of Police Lodge 1. "The only ones suffering from this are the officers. It's Christmas. It seems like Ramsey is out of answers about how to address the crime problems."

Although homicides have surged in recent weeks, the District's tally of 182 killings so far this year is one fewer than for the same period last year. The city remains on pace to have fewer than 200 homicides for the second year in a row, the first time that mark would be achieved since the mid-1980s.

Police have grown increasingly concerned about a rise in robberies in all quadrants of the city. Robberies jumped from 284 in July to 475 in October. Police increased patrols, and robberies dipped last month to 376 reported cases.

The four people were killed within six hours of one another.

The violence began at 11:10 p.m. Thursday when the 17-year-old was shot at 14th and Chapin streets NW, police said. The youth, identified as Norman Jenkins of the 2300 block of 15th Street NW, was shot several times when he refused someone's order to remove his ski mask.

A half-hour later, the 55-year-old man was shot to death after an argument in the 4600 block of Blaine Street NE. Police did not release his name because his relatives hadn't been notified.

Police officials said last night that they had arrested someone in the case but did not release the suspect's name. The victim and the suspect were smoking PCP and got into a fight over $5, police said.

The third killing occurred about 1:30 a.m. in what police described as a robbery attempt in the 2000 block of Savannah Terrace SE. Elexius Woodland, 24, and a friend were walking away from a convenience store, where they had bought food, when at least two men in a dark car approached them. The men demanded money and one fired a handgun, police said. No money was taken.

Woodland, who lived nearby, died after being wounded in the face and stomach, authorities said. The other victim was wounded in the arm and treated at a hospital for injuries that weren't life-threatening.

Three hours after Woodland was slain, police found the body of William Carlton, 33, who was shot to death in the 1200 block of Eaton Road SE, police said. Investigators said Carlton lived in the 3300 block of Wheeler Road SE.

Police urged anyone with information about the homicides to call detectives at 202-727-9099. Police offer rewards of up to $25,000 for information in homicides.