MIA Search a Painstaking Process : Vietnam: Despite diplomatic ties and increased cooperation, it may take years to piece together fates of U.S. servicemen.

HANOI — Two weeks ago, a teen-ager walked into a villa on the outskirts of this capital with a strange tale: In his village in the northern province of Son La, he had overheard a neighbor telling how he had buried two American pilots who had crashed in the war more than 20 years ago.

The yellow stucco villa is known to its inhabitants as “The Ranch,” and such stories are not unusual there. It is the headquarters in Vietnam of the Joint Task Force-Full Accounting, the branch of the Defense Department charged with trying to resolve the fates of more than 2,200 servicemen still listed as missing in the Vietnam War.

When the teen arrived at The Ranch, he was interviewed by a Vietnamese-speaking U.S. investigator. Less than 14 days later, an excavation team, made up of American experts and officials of the Vietnamese ministries of defense and interior, was at work in the remote village and has reported finding the “possible remains” of a human at the grave site.

“This would not have been possible even two years ago,” said Lt. Col. Timothy G. Bosse, commander of the task force, marveling at the speed with which the excavation team was redeployed from central Vietnam to the north. “We’ve come a long way.”

This high degree of cooperation with Vietnam was cited by President Clinton on Tuesday when he announced that he was normalizing relations with Hanoi after 41 years. “With this new relationship, we will be able to make more progress,” Clinton said.

Even with formal relations, however, the process of determining the fate of each missing U.S. serviceman is a herculean task that may take many years to accomplish.

Every year, the Americans and the Vietnamese conduct what are known in military parlance as JFAs, or “joint field activities,” in which teams of American experts--translators, anthropologists, morticians--are sent from Hawaii to excavate suspected crash sites or investigate reports about possible sites.

There are now 107 U.S. servicemen divided into eight teams who are in Vietnam for a month of searching, the 36th mission since cooperation with the Vietnamese began in 1986. It is expected that they will carry out just 12 excavations and 37 investigations.

There are 1,618 servicemen still listed as missing in Vietnam, with the rest in Cambodia and Laos.

As the Defense Department works its way down the list of reported crashes, the sites seem more and more remote, often high in the mountains of central Vietnam.

“We are going to places even Tarzan wouldn’t go to,” said Maj. Randall F. Garrett, the unit’s operations officer.

Of the outstanding cases, about 400 servicemen were reported missing over water, which means that “resolving those cases will be very hard,” Bosse said.

The Pentagon might speed processing of the list of the missing by adopting a new category: remains not recoverable. A decision on that is still pending.

All but 55 of the 1,618 servicemen have been confirmed dead by the Defense Department, but they will all remain on the list of the missing until their bodies are found. The 55 are known as discrepancy cases because they were last seen alive, for example after parachuting to safety, but there is no explanation as to what happened to them.

Even with the benefit of a preliminary investigation, following up a crash that happened 25 years ago can be a daunting task. The teams use window screens to filter dirt, looking for any evidence that will help establish the death of an American--not only bone fragments but watches, dog tags and scraps of clothing.

“If we’re off by a couple of feet, we might as well be off by a couple of miles,” said Bosse.

Finally, when the searchers get to “undisturbed sterile soil,” the anthropologist on the team will make a determination to call off the hunt.

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Garrett said that, since he arrived in Vietnam in September, “it is rare when you don’t turn up some remains.”

Once remains and effects are recovered, they are handed over to an anthropology team of U.S. and Vietnamese experts to determine if they are human and if they could be American. The remains are forwarded to U.S. laboratories in Hawaii, with full military honors.

There have been 66 positive identifications of American servicemen since the joint task force was established in January, 1992, when it took over from the Joint Casualty Resolution Center based in Bangkok, Thailand.

Bosse, who took over command of the task force last month, said that, besides helping on the ground, the Vietnamese were improving the quality of their research into archives that contain information about downed pilots.

Prime Minister Vo Van Kiet vowed Wednesday to continue the cooperation, pledging that Vietnam would do its “utmost in working together with the United States toward the fullest possible accounting of the American MIAs in the Vietnam War.”

Besides the task force’s efforts, another group of investigators, who are attached to the Defense Intelligence Agency’s office in Bangkok, devote their time to following up reports of “live sightings” of men who could possibly be surviving prisoners of war. The Vietnamese have denied that such prisoners exist, and there has never been a proven case.