The fatal shootings of three people last night brought the number of slayings in Washington this year to 454, surpassing the total for last year and dashing the hopes of city leaders who had looked for a continued downturn in violence.

Last year's total number of homicides, 451, represented the first decline since a wave of killings began building in 1986, but 1993 has proved to be a bloody year that will become at least the third worst ever for homicides in the District, after 1991 and 1990.

Two of last night's slayings happened about 7:30 p.m. in Congress Heights in Southeast Washington, when a 19-year-old man and his 14-year-old sister were shot in a car, police said. The third occurred about the same time, when a man was fatally shot in the Benning neighborhood of Northeast Washington.

The slaying that raised the number of homicides to last year's total, 451, occurred Thursday night on a crime-plagued street north of Mount Vernon Square.

It had much in common with many of the year's other killings: Police said they suspected it was drug-related. It involved a gun, occurred before midnight, and its victim, identified by police as Terry Hunter, 19, was a young black male.

"Guy gets shaken down; guy gets shot," said one investigator familiar with the Hunter slaying. "It happens all the time."

The slayings are being investigated by a homicide unit burdened by crushing caseloads and sagging morale.

Once again this year, neighborhoods forming an arc across the eastern side of the city bore the brunt of the killings. More than half of the deaths occurred in the three diverse police districts that include the middle-class neighborhoods of Brookland and Stanton Park as well as the working-class and poor communities of Marshall Heights and Washington Highlands.

D.C. police often found their resources strained by big bursts of gun violence, one of which left nine people dead in two days. Investigators said much of the shooting occurs between loosely knit groups of young men feuding over drugs and turf.

D.C. Mayor Sharon Pratt Kelly and Police Chief Fred Thomas, as had their predecessors, repeatedly promised swift, tough responses.

Kelly ended last December with an upbeat news conference on the decline in the number of killings. "To have a 7 percent decrease in the last year, we feel is a great milestone," she said. By this October, she was asking President Clinton for authority to call out the National Guard to help control violent crime.

The mayor, who was in Las Vegas yesterday for an event connected to the World Cup soccer tournament, was unavailable for comment.

Thomas announced a series of initiatives, creating a violent crimes and gang task force and other special investigative squads and doubling street patrols in high-crime neighborhoods through the use of overtime. Nonetheless, the rate of slayings increased.

"I'm not running the flagpole up and saying all is lost," Thomas said when interviewed yesterday during a conference call with City Administrator Robert L. Mallett. "I am still encouraged {that} we will not surpass our deadliest year or second deadliest year."

The violence that has torn through the District this year has felled adults, teenagers and young children.

In late September, 4-year-old Launice Smith was fatally wounded at a pickup football game behind Weatherless Elementary School in Southeast Washington's Greenway neighborhood in a spray of gunfire that also killed the man who was the intended target.

Three months earlier, six children at the public pool at the Benning Park Recreation Center in Northeast Washington were wounded by a gunman firing into the crowd from a nearby hilltop.

For nearly two months, two Northwest Washington neighborhoods, Mount Pleasant and Columbia Heights, were terrorized by a man who drove his car along neighborhood streets, stopped and fired a shotgun at passersby.

A suspect, James E. Swann Jr., 29, was caught on April 19, but by that time, four people had been killed and five others seriously wounded in 14 apparently indiscriminate attacks.

So far this year, nine merchants or employees have been slain in store robberies and three others wounded, including one man who was left paralyzed. Fifty-two people have died in robberies this year.

For several days in October, television news programs showed a security-camera videotape of a pistol whipping, robbery and shooting at a jewelry store in the Shepherd Park section of Northwest Washington that is owned by a Vietnamese American family.

"Apparently, 1992 was just a flash in the pan, and now we are back on a bad track," said James Foreman, coordinator for the Metro Orange Coalition, which is made up of citizen anti-crime patrols.

Thomas said his anti-crime initiatives have produced results. He said, for instance, that compared with 1992, homicides were down in six of 11 months through November.

At the same time, however, the chief said crimes such as homicides, rapes, assaults and robberies were up 1 percent, compared with the number this time last year.

"The initiatives will pay large dividends as we move into calendar 1994," Thomas said. Overall, crime in the District, he said, has decreased by less than 1 percent, compared with last year.

In restructuring the police department, Thomas has left the homicide unit with fewer resources to investigate more cases.

According to police statistics, D.C. homicide detectives on average handle 13.5 cases a year, compared with the national average of four to five cases a year. Sources said the department is hoping to increase the number of investigators in the homicide division from about 50 to 110 in the next year.

Some detectives have been transferred from the homicide division to special task forces designed to combat violent crime, but it is still the leading unit in responding to slayings.

The division lost five detectives, two sergeants, a lieutenant and a captain when Thomas created the 110-member violent crime and gang task force in October to investigate nonfatal shootings, stabbings and beatings in the 7th and 5th districts, on the northeastern and southeastern sides of the city, respectively. It lost six more detectives to a special squad assigned to investigate slayings just in the 5th Police District.

Thomas is considering a proposal from the homicide division to assign all detectives to particular police districts throughout the city. "This would cut down on them having to run all around the city to investigate cases," said one homicide source familiar with the proposals.

The unit is also proposing that detectives be provided with cruisers that they can take home after their shifts as part of an initiative to boost morale and improve efficiency.

On Monday, two retired homicide detectives returned to the squad to train the dozen new investigators who joined the homicide division in late September.

The two veterans were brought in to compensate for the drain that occurred as seasoned detectives retired from the squad or were reassigned to various task forces, said Inspector William O. Ritchie Jr., commander of criminal investigations. For six months, Robert Chaney and Raymond "Jeff" Greene will work with novice investigators in the office and at crime scenes.

In one of last night's two fatal shooting incidents, the man and his sister were killed while in a white Datsun 280Z that was northbound on Martin Luther King Jr. Avenue at Randle Place SE.

Violence is not uncommon in the surrounding Congress Heights area. "It is another typical Christmas for this neighborhood," said an employee at a nearby store who heard the gunfire.

The victim in the other fatal shooting incident was a man who was working under the hood of a white Pontiac when he was hit by several bullets.

Police said one of the shots apparently ricocheted off the hood and through the upstairs bedroom window of a neighboring row house, where it lodged in the ceiling.

Inside that house, Calvin and Maxine Thompson were decorating their Christmas tree. "I am so shook up, I don't know what I want to do here," Calvin Thompson said.

No information about motives or possible suspects was available in either incident.

About the Thursday night shooting, investigators said Hunter, of the unit block of Galveston Street SW, near the southern edge of the city, was walking with several friends on the 1200 block of Ninth Street NW when they were approached by at least two other men.

The men demanded money from Hunter, who handed an undetermined amount to them, investigators said. When they asked for more and Hunter said he had given them all he had, one of the assailants pulled out a small-caliber handgun and shot him in the head and chest, according to investigators.

Police said they believe that the dispute was over a drug debt. They have made no arrests in the case.

The block where the shooting occurred is a collection of old brick buildings, boarded-up storefronts and trash-strewn lots. Drug dealers, neighbors said, are never far away.

Martin Castro, 20, who lives at Ninth and M streets, said he heard the shots that ended Hunter's life but didn't bother to call police. "It's the third night in a row that we have gunfire in the block," he said shortly after the shooting. "I used to call 911, but the police officers just show up, pop into the liquor store, ask a few questions and leave."

"Things just seem like they are getting so much worse," said Mary Sanford, who leads a citizen patrol called the Fed Up Coalition near the Manor Park neighborhood of Northwest Washington. "I don't see the police initiatives making any difference against the hoodlums out there shooting on the streets and in drive-bys."

Staff writers Mary Pat Flaherty, Keith A. Harriston, Wendy Melillo, Brian Mooar, Santiago O'Donnell and Martin Weil contributed to this report.