It has been almost 20 years since the first young prostitutes, juvenile runaways and hard-luck teenagers began to disappear here along this stretch of highway near the airport known as the Strip. In a hard, cold rain today, it is still a rough place where desperate women ply their trade -- but once, it was known as "a hunting ground" for a committed, wily serial killer.

Two weeks ago, police arrested a man named Gary Leon Ridgway, 52, for loitering for prostitution here. Unbeknown to the vice unit, a decades-old sample of Ridgway's saliva was being analyzed that tied the truck painter's DNA, authorities announced Friday night, to one of the most sensational, unsolved serial murder rampages in American history.

Between 1982 and 1984, a predator dubbed "the Green River killer" is believed to have abducted, sometimes raped and then murdered by strangulation and perhaps other methods 49 women. The youngest was 15. Most of the victims had not reached their 21st birthday.

The killer dumped his first victims into the Green River, their bodies weighed down with rocks. The river runs close to the Strip.

Later, the assailant chose other sad graveyards, in the trashy woods along roadways between Seattle and Portland. Many of the victims' bodies were so decomposed upon their discovery that they were listed in police files as "Jane Does" and "Bones No. 37" and so on. Most of the victims, reduced to skeletal remains by the rain and vermin, were ultimately identified only by dental records.

King County Sheriff Dave Reichert, who was one of the original detectives assigned to the Green River slayings and was in the woods along the river when the first bodies were found, was careful not to proclaim the case solved.

But he came close.

"This has got to be one of the most exciting days of my entire career," Reichert told a packed news conference Friday evening. "This is not only an exciting day for the people who worked the case, but I know the community has got to be as excited about this as we are."

Ridgway, a Navy veteran who has worked for the Kenworth Truck Company as a painter for 32 years, will be formally charged next week with the murders of four women.

Reichert said that Ridgway had long been "one of the top five suspects" in the murders but that authorities lacked proof.

The new evidence that led to Ridgway's arrest Friday afternoon was old evidence reexamined by ever-more sophisticated DNA analysis. In 1987, Ridgway provided investigators with a sample of his saliva by chewing on a piece of gauze. DNA in the saliva sample was reexamined by a state crime lab several months ago and compared with DNA in semen recovered from three of the victims.

"And guess what?" Reichert said. "The charts were all the same."

But this is not the first time a prime suspect has emerged in the Green River killings. Other names have emerged, and lawsuits charging defamation and slander have been filed.

Ridgway's court-appointed lawyer, Todd Gruenhagen, cautioned reporters not to assume anything, though he has declined to discuss the case.

Ridgway has long been seen as a possible suspect. He was accused in 1980 of choking a prostitute he picked up along the Strip, but the case was dropped after he said the woman had bitten him. In 1982, he was convicted of soliciting an undercover female officer impersonating a prostitute.

A year later, he was a suspect in the disappearance of another woman, and police searched his home but found no evidence linking him to a crime. That woman has never been found.

Ridgway took two polygraph tests in 1984 and 1986 and passed them both, at least to the satisfaction of investigating officers.

Seattle-area law enforcement authorities have weathered years of criticism for their handling of the Green River case. Even lead investigators in the case have admitted that they reacted slowly and did not realize the magnitude of the serial killings at the time they were occurring.

By the time the murders suddenly stopped in 1984, the first task force to investigate the murders had only just been formed.

But once the Green River task force -- which focused the energies of dozens of local, state and FBI agents -- was organized, it consumed massive resources and spent more than $15 million on the case. The investigators employed botanists to compare plant matter; entomologists to wonder about insect consumption of the corpses; anthropologists to do reconstructions of faces from skeletons; psychologists to produce profiles of possible suspects; and even a psychic.

The Green River task force also sent an officer to interview Ted Bundy, the notorious Florida killer, in the hours before his execution to learn more about the thinking of a serial killer.

Task force officers also participated in a two-hour television special dubbed "Manhunt Live" in 1988, which was a precursor to reality TV shows like "America's Most Wanted" and "Cops."

In its work, the task force produced several profiles of the Green River killer. One theory held that he was a law enforcement officer or someone close to law enforcement -- a police officer or a security guard or someone who posed as an officer.

One FBI profile, as described by the Seattle Times, stated: "He has very strong feelings of inadequacy. . . . He has felt that he has been burned or lied to and fooled by women one too many times. . . . Women are no good and cannot be trusted and he feels women will prostitute themselves for whatever reason. When he sees women openly prostituting themselves, this makes his blood boil."

Other profiles, some based on evidence at the crime scenes and the histories of past serial murderers, suggested that the Green River killer smoked cigarettes and drank beer, was in his late twenties or thirties and had "a nagging mother."

Neighbors of Ridgway today described him to reporters as a pleasant, "nice guy" who chopped wood for his fireplace, doted on his second wife, walked his poodle and did not attract much attention.

At his job, some of his co-workers years ago had started calling him "Green River Gary" because it was widely known he had been interviewed by police for possible ties to the crime. But none of the co-workers seemed to think much about it.

One of the steep obstacles in solving the Green River killings is the fact that the victims were often women who lived on the edges of society: They operated under false names, some engaged in prostitution, and they were transient.

Another problem: The killer chose his burial grounds well. Most of the bodies were not found for months or years, and in the rainy Seattle climate, the victims were quickly reduced to bones, with scant physical evidence to help police decode their deaths.

Why did the Green River killer suddenly stop in 1984? That is a question that has baffled investigators. Some officials, before the arrest of Ridgway, thought the killer might have died, or had been arrested, or was jailed on unrelated charges. He might have stopped because of increased use of police "decoys" along the Strip who were arresting and interviewing customers of prostitutes.

Now, they are not sure. Another serial killer might have been plying his or her trade a few hours' drive north in Vancouver, British Columbia. There are dozens of unsolved serial slayings around the West.

Investigators remove the body of Wendy Lee Coffield, the first victim found of the Green River killer, on July 15, 1982.MARCIA CHAPMANCAROL CHRISTENSENCYNTHIA HINDSOPAL MILLSGary Leon Ridgway, a longtime suspect in the serial slayings, will be formally charged this week with the murders of four women.