Authorities in the Washington region spotted the same faded blue 1990 Chevrolet Caprice and recorded its New Jersey tags on at least 10 different occasions this month, but saw no reason to link it to the sniper attacks until this week, law enforcement sources said yesterday.

Ten times, authorities thought the car warranted enough suspicion that they ran its license plate number through a national police database, sources said. Each time, however, they let the driver go after finding no record that it had been stolen or that its occupants were wanted for any crimes.

Police said the weather-beaten Chevrolet with whitewall tires didn't attract closer scrutiny because they were mistakenly fixated on other vehicles -- a white van, a box truck, a cream-colored Toyota.

"We were looking for a white van with white people, and we ended up with a blue car with black people," said D.C. Police Chief Charles H. Ramsey, whose department ran the Caprice's tags on Oct. 3, just hours before a fatal shooting in the District that has been tied to the sniper suspects, John Allen Muhammad, 41, and John Lee Malvo, 17.

Before the suspects themselves dropped the clue that led to their arrests, the thousand or so agents and police officers working the case were painstakingly chasing tips and leads that led nowhere, many of them said.

"We were running a lot of leads into the ground," said one local law enforcement source. "There were a ton of dead ends."

Some of those might eventually have paid off, but none with the speed that the suspects' own tips provided.

One of the more promising trails involved motels along the shooting path. Authorities combed through guest lists and later determined that Muhammad and Malvo had stopped for the night near the shootings in Spotsylvania and Prince William counties, as well as one outside a Ponderosa Steakhouse in Ashland, Va. In all, Muhammad and Malvo are suspected of shooting 13 people, killing 10 of them.

The two suspects were spotted at a YMCA on Route 1 -- less than a mile from the Ponderosa -- in the days before the Ashland shooting, according to police and YMCA officials in Richmond. Other guests said the pair stood out because they were unusually dirty and eager to use the YMCA's showers.

Some task force members predict that those coincidences might eventually have led to arrests, but acknowledged that they were a long way from that point.

Until the suspects dropped the hints that led to their arrests, the investigation was mostly characterized by frustration.

"We were chasing the nut of the day," one investigator said.

Then, on Oct. 17, a man claiming to be the sniper called the Montgomery County police department's public information office, sounding frustrated and piqued. Apparently upset that he was not being taken more seriously, the caller said he was involved in a fatal shooting "in Montgomery" and urged agents to check it out.

Police said they believe the man called them a second time, but that conversation did not last long because he was dialing from a pay phone and ran out of change, sources said.

On Oct. 18, a Virginia priest received an eerily similar call from someone professing to be the sniper. The Rev. William Sullivan of St. Ann's Roman Catholic Church in Ashland told authorities that the caller spoke about a robbery-murder in Montgomery, Ala., a telling detail that caught investigators' attention.

The Alabama killing ultimately led to a fingerprint and the two suspects.

Another fat clue fell into agents' hands Oct. 19, after the shooting in Ashland.

Tacked to a tree near the crime scene was a three-page handwritten letter, adorned with stars, that berated agents for "incompitence." Specifically, the author accused agents of bungling at least six separate phone calls that the self-proclaimed sniper had placed to authorities.

"These people took [the calls] for a Hoax or a Joke, so your failure to respond has cost you five lives," the letter stated menacingly.

The letter also led them to the priest, who related his own experience talking to the sniper.

In retrospect, investigators said yesterday that they believe they unwittingly came close to finding the sniper on other occasions, but failed to corner their quarry because their vision was clouded by thousands of other leads that turned up empty.

Perhaps the best opportunity came on Oct. 3, immediately after the sniper fatally shot a 72-year-old man waiting for a bus in the District, near the Montgomery County border.

About 10 seconds after the shooting, a witness saw a dark-colored Chevrolet Caprice creep away from the scene with its lights off. The witness later reported the sighting to police.

Another witness, a restaurant employee in the area, said in an interview that he also saw a Caprice slowly driving away but did not volunteer the information to police until after the suspects were arrested because he assumed agents were looking for a white van.

"At that time, I didn't know that that [the Chevrolet] was important," said the restaurant worker, who spoke on condition of anonymity. "It was the situation and the timing, and I didn't know if I wanted to get involved. And everybody's 'white van' this, 'white van' that."

Four days after that shooting, D.C. police issued a teletype asking officers to look for "an older model Chevrolet Caprice," but it was described as burgundy-colored.

Witnesses saw a Caprice with its lights out, Ramsey said, but they also saw a burgundy Toyota Camry speed away and may have confused the two and come up with the wrong color.

In an Oct. 13 interview on CNN, Montgomery Police Chief Charles A. Moose was asked about the report of a Caprice leaving the scene of the slaying in the District. Moose said task force investigators were aware of the sighting, but he played it down, saying there was "not a big push for public feedback on that."

Ramsey noted yesterday that D.C. police never gave up on the possibility that a Caprice was involved and reissued the alert 10 days ago.

The police sightings of the Caprice began as early as Oct. 3, the deadliest day of the shootings, when a Montgomery County patrol officer took note of the car for unknown reasons but found no basis to detain the driver or write a ticket. A District officer would also run the tag that day.

On Oct. 8, a Baltimore police officer stopped the Caprice and interviewed the man at the wheel, John Allen Muhammad, but sent him on his way. The car was seen again in Baileys Crossroads in Fairfax County and then on Oct. 21 at Tysons Corner, where a red-light camera snapped its picture.

The car sightings were not the only missed opportunities for law enforcement during the three-week hunt for the sniper.

Ten full days before the sniper attacks began in Maryland, one of the two suspects in the case left his fingerprint on a magazine at the slaying scene in Montgomery, Ala., police said.

But investigators were unable to link the fingerprint with a name -- Malvo's -- until a month later because of delays in processing the evidence. By that time, all 13 shootings in the Washington region had occurred.

Some authorities speculated that if Malvo had been linked to the Alabama crime before the sniper shootings, the Caprice might have drawn more suspicion. Detectives might have linked Malvo to Muhammad, and the car is registered to Muhammad.

But the fingerprint was sent to the Alabama Bureau of Investigation for processing, according to federal officials in Washington. The ABI is set up to run prints only against state criminal records, federal officials said. The original print was not forwarded to the FBI for comparison with federal fingerprint records, the officials said.

After the sniper connection was made, the FBI processed the print in its Integrated Automated Fingerprint Identification System, two officials said. The system includes fingerprints provided by the Immigration and Naturalization Service in deportation cases, the officials said. Malvo's prints were filed there.

Alabama does not subscribe to the FBI fingerprint system, which was created in 1999. Fewer than half the states have signed on as participants, officials said.

Montgomery County State's Attorney Douglas F. Gansler discusses the sniper case. With him are, from left, Deputy State's Attorneys Katherine Winfree, Gayle Driver and John McCarthy.