D.C. police officials yesterday took the extraordinary step of blanketing large swaths of the city with undercover and uniformed officers and requested Park Police and National Guard helicopters last night after days of violence that included the killing of a grandmother and the shooting of a mother and her baby Friday night.

Chief Charles H. Ramsey announced that the equivalent of 300 more officers would patrol the troubled neighborhoods last night as part of the city's effort to quell the perception that violence in the nation's capital is out of control.

"We have got a situation on our hands where we really have to take some swift action," said Ramsey, who held a news conference with the mayor's chief of staff, interim city administrator and spokeswoman. "I am outraged, like the community is outraged."

Four bystanders were shot in Columbia Heights on Friday night when a gun battle between what police said were feuding Hispanic gangs broke out after a party at the Latin American Youth Center. The mother and her 5-month-old boy were shot while sitting on an apartment building stoop in Southeast Washington when two masked men suddenly appeared and opened fire. A man sitting next to them was killed.

"She had the baby locked to her chest, hysterically screaming," said Jerry Tyler Sr., the resident manager of the building in the 1600 block of 29th Street SE. The baby is in critical condition at Children's Hospital, and the mother is in stable condition at another hospital.

The string of shootings represents the first challenge of its kind for Mayor Anthony A. Williams (D), who was elected in November vowing to transform the tarnished image of the District -- which had the nation's highest homicide rate earlier this decade -- into that of a well-run city where residents and visitors could feel safe.

"I'm deeply concerned about the recent gun violence in our neighborhoods," Williams said in a written statement. "I'm especially saddened when our little babies and parents and grandparents are wounded and killed. That is not acceptable in the District of Columbia."

The mayor went last night to Columbia Heights, where he spoke of the need to redouble efforts in combating crime, before heading to the scene of the baby's shooting.

At least three shootings were reported in the city by late last night. In one, a man was shot in the foot about 10 p.m. at Minnesota and Pennsylvania avenues SE. Later, a man was shot in the chest in the 4000 block of Livingston Road SE. Also, a man was shot in the leg about 11:35 p.m. in the 4000 block of Minnesota Avenue NE, near the Minnesota Avenue Metro station.

Executive Assistant Police Chief Terrance W. Gainer said yesterday that he required officers from day shifts that usually end about 3 p.m. to stay four hours later and officers from the midnight shift to come in three hours early to get more officers on the street in the 3rd, 4th and 6th police districts.

"We're going to supersaturate this baby," Gainer said.

The shootings in Columbia Heights and in Randle Highlands caught the District police force by surprise on a night when there apparently was a shortage of officers on the streets. "I thought we had the right amount of people out, but even as late as 11 p.m., our priority calls were backed up because we had no cars available," Gainer said.

A shortage of officers -- and vehicles -- on patrol has been a chronic problem for the department for years. A decade ago, when the crack cocaine epidemic pushed the District's annual total of slayings up to 434, there were about 4,800 officers on the force. Now, when the city has about 300 slayings a year, the department has about 3,600 officers -- about 25 percent fewer.

The string of eight shootings Friday night did not surpass the number on some of the District's bloodiest nights in the late 1980s and early 1990s -- or even this year, when 12 people were slain over four days. But last week was one of the first times that Ramsey, like Williams, has faced a highly publicized wave of violence since he arrived here 14 months ago as homicides and reported crime were declining.

Ramsey has said often that he's not just trying to reduce crime but also the fear of crime.

"Homicides are slightly down from the years before, but this is still totally unacceptable," Ramsey told reporters at the 6th District. "Our goal is to dismantle the gangs in the District of Columbia. . . . This has gone on for far too long. It's time it stops, and it stops now.

"These people had better understand that. The days of them being able to just shoot up and down the streets is over. These little street thugs out there committing crimes randomly, shooting, causing injuries to innocent bystanders . . . has to stop."

The first gunshots on a warm Friday night rang out about 9 p.m. in Columbia Heights, when the streets were filled with residents. Police officers said there were so many people outside, it felt like daytime.

"The city was abuzz," Gainer said. "It was as busy as I've seen it in the last year. Traffic was heavy, people were pouring out of restaurants and bars, and the hustlers were all out. We had our hands full."

On Columbia Road, an ex-boyfriend of a woman confronted her new boyfriend on the balcony of her house, police said. He accused the new boyfriend of beating the woman, and they argued. The new boyfriend allegedly pulled out a handgun and shot the 28-year-old man, who stumbled outside and collapsed on a bench. He was treated at Howard University Hospital and released. Mauritoure Dembele, 19, of the 1300 block of Columbia Road, was arrested and charged with assault to kill while armed, police said.

Only minutes after that shooting, gunfire erupted a block away, where there was a party at the Latin American Youth Center to mark the end of the school year. Merengue music filled the center's basement recreation room, and about 55 teenagers spilled out onto the sidewalk, said Mai Fernandez, the center's director.

Outside, police said, two rival Hispanic gangs, well known to the police, were arguing. One gang calls itself "BU" or "Brown Union" and is composed of youths who operate in the Columbia Heights and Mount Pleasant neighborhoods, but mostly around 14th Street and Park Road NW. The other gang, which goes by the name "La Mara R" (mara is Spanish slang for "clique"), hangs out around 17th and R streets NW but roams around Adams-Morgan, Columbia Heights and the Cardozo neighborhood, police said.

The shooting began after members of the Brown Union accused members of La Mara of plotting to jump the brother of a Brown Union member, police said. A Brown Union member then started shooting, according to Sgt. Jose Bimbo, who was on the scene Friday night.

"It was chaotic," Bimbo said. "There were people all over the place." The bullets hit four people -- two women and two men -- standing on the street, he said.

The four, whom police would not identify because they are witnesses, were all shot in the legs. They were taken to Howard University Hospital, treated and released.

"They were just innocent bystanders," Bimbo said. "We have nothing to associate them with the gangs."

Across town in Randle Highlands about 11 p.m., in the 1600 block of 29th Street SE, some people were sitting on the front stoop of a four-story brick apartment building when two masked men appeared, police said. One had a shotgun, the other a handgun. They apparently aimed at Millard C. Sauls, 25, of the 5000 block of Call Place SE, hitting him several times. Shots also struck a 22-year-old mother and her 5-month-old boy.

"I heard her scream, `My baby, help my baby,' " said Theresa Miller, who watched from her window after the shooting.

"If you wanted to leave, you had to step over a whole puddle of blood," said neighbor Tony Myers.

Sauls died at D.C. General Hospital. Police said he was the intended target. They said he had been arrested two years ago in the District on a charge of assault with a dangerous weapon and was wanted in Sacramento on armed robbery charges.

The mother, who police said was an acquaintance of Sauls, is in stable condition with gunshot wounds to her legs and buttocks, police said. The baby is in critical but stable condition with gunshot wounds to the leg and stomach.

On Monday, a gun battle claimed the life of Helen Foster-El, 55, who was shot in the East Capitol Dwellings in Southeast as she tried to usher neighborhood children to safety. Yesterday, police arrested Kent Claude Chambers, 20, a fourth suspect in that case, who turned himself in. An arrest warrant had been issued charging him with assault with a dangerous weapon. Police are still searching for more suspects.

Staff writers Allan Lengel and Steven Gray contributed to this report.

CAPTION: (Photo ran in an earlier edition) D.C. Police Chief Charles H. Ramsey and Cmdr. Rodney D. Monroe of the 6th District leave the police station to start on a night of heavy police presence in response to a rash of shootings.

CAPTION: Police Chief Charles H. Ramsey and Mayor Anthony A. Williams walk through Adams-Morgan. The chief and the mayor also visited the site of Friday night's shooting on Columbia Road NW.

CAPTION: D.C. Police Chief Charles H. Ramsey, right, and Rodney D. Monroe, 6th District commander, describe the police response to recent shootings.

CAPTION: Williams and Ramsey visit the Columbia Road NW site where gunfire between two groups of youths after a party wounded four bystanders Friday night.