WASHINGTON - Stung by an outbreak of violence, including eight killings last weekend, police are taking the unusual step of establishing vehicle checkpoints in a crime-ridden neighborhood in the nation's capital.

Starting tomorrow night, officers will check drivers' ID and turn away any who do not have a "legitimate purpose" in the area - a plan that has drawn swift criticism from civil-liberties groups.

The checkpoints come as police try to combat a spike in the number of homicides, which rose 7 percent in the city during 2007 after several years of decline.

Most of last weekend's slayings occurred in the Fifth Police District in the city's northeast, where authorities plan to set up the checkpoints in an area a mile northeast of Union Station. Already this year, the police district has had 22 killings, one more than in all of 2007.

"The reality is, this is a neighborhood that has been the scene of many violent crimes, and something had to be done," D.C. police spokeswoman Traci Hughes said.

The initiative has raised the ire of the American Civil Liberties Union, which plans to watch what happens with the checkpoints before deciding on any legal action.

"This is craziness," Arthur Spitzer, legal director for the ACLU's Washington office, told the Washington Post. "In this country, you don't have to show identification or explain to the police why you want to travel down a public street."

Officers will stop motorists traveling through the main thoroughfare of Trinidad, a neighborhood of mostly tidy two-story brick rowhouses that includes Gallaudet University and is near the National Arboretum.

Police will ask motorists to show proof they live in the area. If they do not have proof, drivers must explain whether they have a reason to be in the neighborhood, such as a doctor's appointment or a church visit.

Police will search cars only if they observe the presence of guns or drugs, officials said. Anyone who does not cooperate will be arrested.

The checkpoints will be enforced at random hours for at least five days, though they could be extended to 10 days, police said.

The Washington Post said that the initiative would involve stopping vehicles approaching the 1400 block of Montello Avenue NE but that the strategy was not airtight. There are many ways to get in and out of Trinidad, not just on the one-way Montello Avenue. And pedestrians will not be stopped, a factor critics say might render the program ineffective.

District of Columbia Council member Harry Thomas Jr., who represents Trinidad, said he was worried about a potential backlash from angry residents, many of whom question whether the checkpoints will reduce violence.

"Do you want to go home every day and prove that you live at your house?" he asked.

Still, Thomas said, he is taking a wait-and-see approach, noting that many of the recent shootings involved people who drove into the area to buy drugs or settle scores with residents. The checkpoints should make it more difficult for outsiders to come in, he said.

Yesterday, city officials downplayed the significance of the initiative, noting that police had used various checkpoints in the past.

"It's not unlike a sobriety checkpoint or a traffic-safety checkpoint," Hughes said. "This time, it's to make sure violent crime is deterred as much as possible."

Responding to the threat of a legal challenge, interim D.C. Attorney General Peter Nickles cited a similar case involving New York City police. A federal appeals court ruled in 1996 that those police tactics were constitutional, saying that the checkpoints "were reasonably viewed as an effective mechanism" to reduce drive-by shootings.

In a Supreme Court case from 2000, however, justices struck down random roadblocks used in Indianapolis to screen people for illegal drugs, ruling that they were an unreasonable invasion of privacy. The high court's majority concluded that law enforcement alone was not a good enough reason to stop innocent motorists.