TRURO, Mass., Jan. 7 - In an unusual last-ditch move to find clues to the three-year-old killing of a freelance fashion writer, police investigators are trying to get DNA samples from every man in this Cape Cod hamlet, all 790 or so, or as many as will agree.

Raising concerns among civil libertarians and prompting both resistance and support from men in Truro, the state and local police began collecting the genetic samples last week, visiting delicatessens, the post office and even the town dump to politely ask men to cooperate. Legal experts said the sweeping approach had been used only in limited instances before in the United States - although it is more widely used in Europe - and in at least one of those cases it prompted a lawsuit.

Sgt. David Perry of the Truro Police Department and other law enforcement authorities here say that the program is voluntary but that they will pay close attention to those who refuse to provide DNA.

"We're trying to find that person who has something to hide," Sergeant Perry said.

The killing was the most notorious in this resort community in memory. Christa Worthington, 46, who had lived in New York and Paris and London before retreating to the quiet sea-stung town, was found stabbed to death in her bungalow here on Jan. 6, 2002, her 2-year-old daughter, Ava, clinging to her body.

Semen was found on the body, and in the last three years the police have investigated a former boyfriend and other men, including a married man who is Ava's father.

"All those people are ruled out at this point," Sergeant Perry said.

A $25,000 reward failed to crack the case, which generated international publicity and a lurid book, "Invisible Eden," by Maria Flook, with explicit details of Ms. Worthington's love interests and violent death.

So the police sought help from the F.B.I., which said it thought the killer had Truro ties and suggested trying to match the semen in a global genetic canvass.

"The person we're looking for is the one who deposited the DNA" by having sex with Ms. Worthington before she died, Sergeant Perry said. "We're not saying that this is the killer. What we're saying is we need to talk to this person, who may be just the last person to see her alive."

Stopping in the Highland Grill in Truro on a frigid Friday, Jeff Evans plunked down $2 for a brownie almost as big as a paperback. Then, at the prompting of a state police detective and a Truro police officer parked at the grill's counter, Mr. Evans, 46, a pest exterminator, wiped the inside of his cheek with a lollipop-like cotton swab, capturing a smidgen of genetic evidence to give to the government men. Sam Scherer, 18, another Highland Grill patron, had already done the same thing. So had Jerrid Bearse, 20.

While many residents have cooperated, some have complained that the DNA sweep is coercive.

"I think it's outrageous," said Dick Seed, 44, a Truro sign painter who called the American Civil Liberties Union to complain.

"I really think they're usurping my civil rights," said Mr. Seed, who may know something about DNA because his father is Dr. Richard Seed, the eccentric physicist who drew worldwide attention by announcing seven years ago that he planned to clone humans. "Are they going to chase down everyone who didn't give a sample? It kind of sounds like Stalin's secret police. If there's a murder committed in a restroom, are they going to be asking for a urine sample?"

Mass DNA collection drives, as needle-in-a-haystack as they might sound, have yielded results in criminal investigations in England and Germany. Six years ago in Germany, for example, authorities investigating the rape and murder of an 11-year-old girl collected DNA samples from 16,400 men, a sweep believed to be the largest to date. DNA from one man matched the evidence, prompting him to confess his guilt.

In this country, the technique has been tried in a few places, generally with less success. It is usually used in a more targeted way than in Truro.

In Baton Rouge, La., in 2003, authorities trying to find a serial killer took swabs from 1,200 white men who drove white pickup trucks, but the dragnet did not yield a suspect; a black man was later arrested using other investigative methods. In Omaha last year, the police, searching for a serial rapist, sought DNA from about three dozen black men who worked for the Omaha Public Power District. And in a rape investigation in Charlottesville, Va., the police over the last two years have asked for swabs from about 200 black men.

These investigations have been contentious, especially when the authorities hold on to the DNA of people found to have no connection to the crime. Baton Rouge law enforcement agencies are being sued by nearly two dozen of the 1,200 men they tested; the men want their DNA samples destroyed and their genetic information removed from a databank that can be used in investigations of other crimes.

"They're not very effective and they're certainly not voluntarily," said Barry Steinhardt, director of the technology and liberty project at the American Civil Liberties Union. "It's either give a sample or you're a suspect. It turns the classic American concept of innocent until proven guilty on its head."

Figuring that the winter population of Truro would be similar to what it was three years ago, investigators chose the days around the anniversary of the killing to begin passing the hat for DNA all over town.

When this summer resort gets a whiff of winter it contracts like a rubber band, leaving only a handful of hangouts open for business. They are places like Dutra's Market, the Filling Station deli, the town dump and the post office, a daily stop for many Truro residents because they do not have home mail delivery.

Since Wednesday, two-person police swab squads have sidled into sub shops and perched by the postal counter, seeking a donation from anyone with a Y chromosome.

The investigators are intentionally mild-mannered in their queries, asking for help, not threatening retaliation. Sometimes they display a photograph of Ava, who is now 5 and living with her mother's friends, and ask the men to help solve the investigation for Ava's sake. They ask the men to sign a card giving their birthday and race, and they ask if the men knew Ms. Worthington or her relatives, some of whom have lived here for years. They take down the license plate numbers of people they approach. They say they may start soliciting DNA in neighboring towns, too, like Wellfleet and Provincetown.

The police found 75 volunteers on the first day alone, Sergeant Perry said. But they have also been rejected by men who say they are offended or uncomfortable.

"Sorry, I just don't like to be around cops," Virge Peres, 28, told Christopher Mason, the state police detective who stopped him at the Highland Grill.

"It's invasive," said Mike McGuinness, 67, at the town dump on Friday. He said he would refuse if asked. "If they have a suspicion of someone and they ask them, that's one thing. But not just doing it willy-nilly."

The police say they will discard any DNA that does not match their sample and will not keep a databank. But several Truro residents, even those who gave their DNA, said they were skeptical of that, as did John Reinstein, legal director of the American Civil Liberties Union of Massachusetts.

Mr. Reinstein said that as of Friday he had received three calls from Truro residents.

"We're very concerned about using DNA sweeps as an investigative tool," he said. "If there's a person out there and has yet to come forward and say he had been with Christa Worthington before she was murdered, that person is not likely to say, 'Test my DNA and see if it matches the crime scene.' From that it seems that what they're looking for is the people who turn them down. So in some way it's saying, 'Will you please come forward and identify yourself as murder suspect.' "

Among the men who gave saliva at the post office was Beau Jackett, a son of Tony Jackett, who is Ava's father and was a suspect early on.

Tony Jackett gave his own DNA soon after the killing and has sold the rights to his story to a California filmmaker. "Most people, I think, agree that they should do whatever it takes to get the guy," he said.

Leo Rose, 49, gave a sample at the Filling Station deli, figuring he had nothing to hide.

"They're not supposed to keep it," Mr. Rose said. "If I did something stupid down the road and they had my sample on file, well, then it's an illegal search and seizure."

Edward Friedman, an older man who hobbles painstakingly, seemed amused that anyone would think he could be a match. "I can barely make it to the car," Mr. Friedman said.

But Craig Hathaway, owner of Dutra's Market, who said he felt he had to allow the police to approach his customers, will not give his DNA.

"Don't get me wrong, I want to see this thing solved as much as the next person," Mr. Hathaway said. "I'm just not sure this is the way to do it."

And Mr. Seed said, "Why don't they just ask me where I was when the murder happened? I was playing poker. What else is there to do here in the winter?"

Sergeant Perry said that aside from the DNA, the police hoped revived publicity about the case would "get people thinking again" about tiny details that might be helpful.

People in this peaceful place are certainly eager to have the crime solved, said Fred Simonin, owner of the Highland, who said some customers had come in just to donate DNA.

"We're not used to having a murderer around," Mr. Simonin said.

Katie Zezima contributed reporting from Boston for this article.