ARLINGTON, Va. - Lit by a midwinter sun, the honor guard paced before the Tomb of the Unknowns, his expressionless face betraying none of the confusion arising over whether one of the bodies beneath the marble slabs now has a name.At the Pentagon, less than a mile from the solemn daily ritual at the tomb, officials were considering Tuesday whether to dig up the half dozen bones of a veteran of the Vietnam War. DNA testing may show the previously unidentified bones to be those of Air Force 1st Lt. Michael J. Blassie of St. Louis, whose A-37 attack plane was shot down over South Vietnam in May 1972."Does the current science enable us with confidence to conclude that the remains in the tomb could be identified?" said Navy Capt. Michael Doubleday, a Pentagon spokesman. "And secondly, if we have a possible association with a specific individual, is it in the best interests of all concerned that we go ahead and do so?"The case, likely to be settled at the presidential and congressional level, amounts to a conflict between two matters of honor among Vietnam veterans: the importance of identifying the dead and returning them to their families versus the desire to have an unknown soldier from Vietnam occupy the military's most hallowed ground alongside the dead from World Wars I and II and Korea."This government has a moral obligation to identify missing servicemembers, and that includes, if appropriate ... veterans in the Tomb of the Unknowns," said Phil Budahn, spokesman for the American Legion. "But that is a major emotional action to open up that tomb and it ought not to be done unless we're very sure that there's no other way to resolve the issue."Sen. Christopher Bond, R-Mo., a member of the Senate Appropriations defense subcommittee, on Tuesday called for a congressional investigation into any area the family wants explored and demanded an explanation from the Pentagon.Rep. William Clay, D-Mo., said that if the Pentagon misled the Blassie family and falsified records of his remains, they acted like "common thugs."Questions have surrounded the anonymity of the Vietnam veteran buried in the tomb as far back as the early 1980s when the sparse remains _ a half dozen bones _ were selected. Unlike previous wars in which hundreds or thousands of unknown remains came home, the thoroughness of rescue and recovery operations and advances in forensic science whittled the number of unknowns down to a handful.So thorough was the work done at the Army's identification lab in Hawaii, writes Philip Bigler in his book about Arlington National Cemetery _ "In Honored Glory" _ that veterans groups were hard pressed to find a body to inter alongside the unknowns from previous wars."It was not until a decade after the end of the war that one body was certified unidentifiable," according to Bigler. In past wars an elaborate ceremony arose out of picking one set of remains from many for burial. Not so after Vietnam. "For the first time since the custom of designating an Unknown Serviceman was established, no selection ceremony was possible."The bones buried at Arlington were found in late 1972 by a South Vietnamese recovery team near An Loc, 60 miles north of Saigon. The site corresponded with the downing earlier that year of an A-37 light attack aircraft piloted by Blassie. Other aircraft, including helicopters and a C-130 had crashed near there. But the jump suit, parachute fragments and inflatable life preserver all pointed to a fighter pilot.In addition, the team recovered some effects that may have included identifying tags. But Doubleday said "those effects, however, did not reach Saigon and have not been in the possession of anyone in the U.S. government since sometime in the immediate hours after the recovery of the remains."While science may make it possible for the bones buried at the Tomb of the Unknowns to be linked through DNA sampling to Blassie's survivors, the ritual of the unknowns may prove a hindrance.To avoid speculation as to the theater or service branch of the soldier buried in the tomb, the military began a tradition after World War I of destroying the selection records. One question the Pentagon must now address is whether some of the items destroyed may have helped establish a link between the remains and Blassie. Another issue is whether the Pentagon in the mid-1980s, in its desire to please the Vietnam Veterans' lobby by finding a set of remains suitable for burial at the tomb, may have overlooked some obvious indicators pointing to the identity of the bones.Like so much else about Vietnam, the issue of burying a veteran at the Tomb of the Unknowns was hotly debated. Most veterans groups wanted equal status for Vietnam alongside America's more successful and popular wars. Those concerned about service members still missing in action, however, worried that the burial ritual would provide closure and end the pressure to fully account for the missing.Even as the Pentagon and the Clinton administration weigh how to handle this case, the military was aware of the longer-term possibility that the tradition of the unknown soldier may be dying."With the ability of science, there may never be another unknown," said Ann Mills Griffiths, director of the National League of Families, a POW-MIA group. "That's not the world's worst situation."