Glenn Miles, a veteran Customs Service patrol officer and a Papago Indian, was gunned down here in late February as he attempted to intercept three drug smugglers headed back into Mexico.

A huge federal manhunt was launched, including the Federal Bureau of Investigation, the Drug Enforcement Administration and the Border Patrol. But the most impressive leads in the case have come from Miles' fellow Papago Customs officers, who spent years with him along this desolate, arid border.

Using the methods their ancestors used hundreds of years ago to hunt game in the mountains and track Apache raiders, Miles' Papago colleagues were able to pick out the tracks of the three suspected killers from among the tracks of thousands of other smugglers of drugs and illegal aliens that crisscross this area.

Miles' friends followed three sets of tracks that crossed near the San Miguel Gate, an unmanned break in the waist-high, barbed wire fence that separates the U.S. side of the Papago Indian Reservation from Mexico.

They also found extensive evidence, not publicly described, that will help identify the suspects. Customs is being deliberately vague about what they found and the methods they used, but the small Papago tribe survived for centuries through its knowledge of its land and the animals that lived there.

Customs Commissioner William von Raab said he thinks that Miles was a victim of a new surge of drug trafficking along the Southwest border in the last year or two as major cocaine and marijuana trafficking groups have sought ways to circumvent increased law enforcement in and around Florida.

Law enforcement officials say that Colombians have moved in along both sides of the border and are working as traffickers and "coyotes," people paid to smuggle illegal aliens into the United States. Von Raab has announced plans to reinforce the border area from Texas to California.

So far the investigation into Miles' death has focused largely on the Valenzuela ranch, a dusty collection of small, dilapidated buildings about 100 yards south of here. Through the squat, scraggly trees, it is visible from the U.S. side.

James M. Smith, who directs the El Paso internal affairs office of Customs, is heading the investigation. He described the ranch as a "staging area for dope and alien smuggling."

Working in cooperation with Mexican authorities, investigators have discovered that on the night of the murder 50 people were at the ranch, including 13 Colombians and two Guatemalans, preparing to enter the United States illegally.

Miles was killed on an unusually mild Friday night in February. As on most nights, he and a handful of colleagues were patrolling a desolate stretch of border covered with dust, scrub brush, cactus and tumbleweeds. The next nearest station for Customs and the Border Patrol is 80 miles away in Lukeville.

From Friday afternoon to Sunday afternoon, the San Miguel gate turns into a kind of no-man's land as Mexicans and Papagos gather at the border for the "flea market."

Authorities say that in addition to the food and clothing for sale, alcohol and many kinds of drugs are openly traded, with participants generally singing, dancing and carrying on for 48 consecutive hours. "You can get anything in the world that you want," one agent said.

Although no alcohol can be sold there legally, the reservation is littered with a sea of brown quart Budweiser bottles -- sold by bootleggers for $2 each -- that twinkle in the hot sun.

The murder occurred just over a mile from the flea market, and the assailants probably would have passed directly through the festivities. But federal agents have not found anyone who was there and is willing to admit hearing the shots or seeing anything unusual.

Miles, 44, was working the 4 p.m. to midnight shift. He was part of a three-man patrol, but his two partners were in a separate car so they could cover more territory. About 9:30 p.m., Smith said, Miles radioed his partners that he saw three backpackers who he thought were carrying drugs.

Smith said smugglers along the reservation use low-flying planes to bring in cocaine, while marijuana is brought in by backpackers who receive $200 to $250 to hike across the border with 60 to 100 pounds. Leon Jaussaud, special agent in charge of Customs' Tucson office, said that the marijuana is then picked up by vehicles and taken to "stash houses" in Tucson before being shipped further into the United States.

Miles checked in again 15 minutes later. By then his partners were speeding toward him to provide a backup. When they arrived, they found his empty truck hidden behind a clump of bushes on the side of the road.

About 100 yards off the opposite side of the road, they saw a light shining. It was his flashlight, which had fallen to the ground beside his body. Miles had been shot several times with two guns.

At the site of his death, there is now a white cross, covered with flowers and surrounded by a small fence that was constructed by his wife, Mary Melissa.

Mary Miles is bitter about her husband's death, but adds that he loved his job and kept his radio on 24 hours-a-day. She said that in the 18 months before his death, her husband had conquered a growing drinking problem and had turned to religion, becoming a Jehovah's Witness. Wanting to legitimize their relationship in the eyes of the church, Miles had insisted on marriage, she said, and the two were wed on Valentine's Day, 1985.

Colleagues say that Miles was proud of the 10 years he had spent with Customs. It was considered one of the best jobs on the reservation. But in some ways his job was a double-edged sword on a reservation beset by unemployment, alcoholism and a general distrust of and contempt for federal authority.

Customs has offered a $100,000 reward for information on Miles' killers, but no one has come forward. Francisco Jose, the tribe's vice chairman, said, "People live out there alone. They're worried about repercussions."

One Customs agent added, "People say they're aware of the reward, but they also say you can't spend it if you're dead."

Customs agents say they have some solid leads on the identities of Miles' killers. Von Raab adds that he is determined to solve the case and to prove that Miles did not die in vain: "We're hiring five people to replace Miles. If they come at us again, we'll hire more. We'll react with more and more force."

There are only 12,000 residents on the 3 million-acre reservation, a land mass the size of Connecticut. Money is scarce, with most jobs involving ranching, basket-making, work for the tribal government and a bingo operation.

Roads through the reservation are lined with small crosses, reminders of the many traffic fatalities, which are often caused by alcohol.

As another sign of the tribe's problems, Mary Miles points to a high suicide rate among the young people. There were nine last year, most by shooting or hanging. A 15-year-old boy hanged himself on March 27 and other attempted suicide the following weekend.

Mary Miles, saying that "suicide is unusual for the Papago," added, "They're getting to alcohol and weed real young -- age 10 and up. That bothered Glenn a lot."

It is no secret that some members of the tribe are involved in the drug- and alien-smuggling that goes on at the border. "I'm sure some of our people get paid off for their cooperation," said Jose, adding that he thinks that the smuggling is "masterminded" by Mexicans and Colombians from across the border.

He said there is a general awareness of the cocaine traffic going on overhead as planes fly through the valleys between rugged mountain ranges "low at night with no lights. It's so apparent, it's kind of a joking thing. If you live out there, you hear them.

"The immediate concern is that if there is a possibility of our own people being involved [in Miles death], we have to ask have we gone that far as a people. We have our own way of dealing with things, but we've never gotten into crime to the point that we would sacrifice one of our own people," Jose said.