WITH U.S. FORCES, SAUDI ARABIA, DEC. 22 -- The small band of Vietnam veterans facing the Iraqi army across the northern border of Saudi Arabia see themselves as having a big stake in Operation Desert Shield. They feel as though they rebuilt the U.S. armed forces almost from scratch, determined that they would never fail again. They believe they have prepared well. Soon they may have the chance to prove it.

Fifteen years after the fall of Saigon, the Vietnam veterans on active service are few and gradually dwindling, but they dominate the upper echelons of the officer and enlisted corps. Army Gen. H. Norman Schwarzkopf, commander of allied forces in Saudi Arabia, heads the short list of Desert Shield military leaders who were in the armed forces the last time the United States mustered more than 400,000 troops on a foreign battlefield.

Today's soldiers are their creation: highly trained, physically fit, all volunteers. They have assembled a professional force of military men and women that, theoretically at least, should present fewer problems -- less bellyaching, malingering, dissent and drug abuse in the ranks -- than their counterparts of that earlier time.

And the battle doctrine is theirs as well: massive strikes from the start meant to achieve a clearly defined objective in the shortest possible time with a minimum loss of life -- and a minimum loss of political will. There will be no dawdling, no soul-searching, they say.

Both today's soldiers and their strategy for war are reactions to Vietnam, a perception by the leadership that failure in Southeast Asia owed itself to a political policy of morale-sapping gradualism in the application of force and a military policy that accepted stalemate as the status quo. This will not happen again, today's leaders say. Today's war may be quick and clean or it may be quick and dirty, but above all, said Marine commander Lt. Gen. Walter Boomer, it will be quick -- and "fairly brutal."

Boomer and other veterans have absorbed the lessons of Vietnam. They take for granted that there will be differences of opinion, but this has become a source of confidence rather than concern. The veterans do not want another Vietnam and have done everything they can to make sure the next war is nothing like it. In this respect, Desert Shield was made to order.

Vietnam was a jungle guerrilla war often fought at close quarters, a light-infantry nightmare of terrifying immediacy. The war against Iraq will rely, certainly at the outset, on massive use of U.S. air power. But the ground war, whenever it may start, will be a sharp contrast to Vietnam, involving tank battles by huge armored forces on both sides in the open desert; a high-tech duel, particularly on the American side, of laser-fired weapons, guided missiles and the risk of sudden, impersonal oblivion.

Politically, Vietnam was a civil war of competing ideologies, ultimately forcing the United States to choose sides against itself. A war in the Persian Gulf, though, would be fought to protect more widely agreed upon U.S. interests against an easily recognized foreign aggressor. That the interests are largely economic does not concern military leaders. What binds them to their task is the commitment of their government to a tangible goal: Get the Iraqis out of Kuwait.

"In Vietnam we did not have a clearly articulated strategy for the use of military force," said Army Brig. Gen. Robert McFarlin, 48, a former adviser to Vietnamese troops and now the support commander of the Germany-based VII Corps. "Here President Bush has described the measure of success in clearly defined terms. We never had that in Vietnam."

Vietnam also was fought mostly by draftees, amateurs -- some of them making the best of a bad situation, some of them reluctant soldiers disgusted and demoralized by a war without end. Desert Shield, by contrast, will be fought by volunteers who say they see military service as an opportunity rather than an obligation. That stated motivation will soon get its toughest test if these volunteer forces are ordered into the most intense combat the U.S. military has faced since Vietnam.

"People ask me, 'Well, how are your guys gonna do? They don't have any combat experience,' " Boomer said. "Well, hell, we didn't have any combat experience when we went to Vietnam, either. There have been relatively few wars in which people have gone into the war with a lot of combat experience across the force."

Still, this new opportunity has created its own problems, the veterans say. After four months in the desert, soldiers are homesick, bored, impatient and uncertain of their fate. Will there be war, and when will it happen? In Vietnam nobody seemed to care, for the clock was running whether a soldier tramped the jungle or cooled his heels in Saigon. He had a year to serve in Vietnam, and all he had to do was count the days.

"Here, people don't know how long they're going to stay," said Air Force wing commander Col. David E. Cormack, who flew 168 combat missions in Vietnam. "The uncertainty is a concern. They would like to know if it's going to last six months, or nine months or what. I spend a lot of time trying to explain it."

But there is no explanation. Desert Shield has no timetable. Soldiers know they are here for "the duration," but they don't know what "the duration" is.

In general, however, the Vietnam veterans seem to have prepared today's soldiers almost as if they had something like Desert Shield in mind. Despite the waiting game, today's volunteer is better trained and presumably more highly motivated and finely tuned for a technologically complicated, fast and possibly ruthless confrontation, where getting it right the first time is likely to be the measure of success.

"It is a little difficult for me emotionally to make comparisons, because I feel very close to the Marines I was with in Vietnam, but I have to do it," Boomer said. "They were good, but overall these Marines are better. They're smarter. We're not taking anybody who's not a high school graduate. I also think they're probably physically stronger overall."

It is not that draftees of the past were bad, said Marine Sgt. Maj. Russell Kendall, 43, who served two tours in Vietnam in 1966-68. "When you were in a predicament, you had to perform -- it didn't take a volunteer or a brain surgeon to know that."

What Kendall and others like about the volunteers is that they have given the leadership an opportunity to build unit cohesiveness, with troops who have walked through the fire together. Instead of trying to integrate untested replacements one-by-one, as in Vietnam, the Desert Shield soldiers have come to Saudi Arabia in units and will leave the same way.

"In Vietnam it wasn't unusual to get a new kid into the unit in the morning and Medevac him out in the afternoon," Kendall said. "Here you know who your next-door neighbor is and what he can do. Everybody is a proven quantity. It gives you a better feeling."

Still, after a platoon takes casualties, strangers will start showing up to replace them, but this is where the new doctrine comes in: The idea is to finish the war before the attrition starts. Today's philosophy puts the best people at the front to clobber the enemy as quickly and as hard as possible.

"With casualties and replacements, it wasn't unusual to have sergeants in Vietnam with one and one-half or two years experience," said Marine Squadron Sgt. Maj. Earnest Jones, 49, an infantryman in Vietnam in 1967-68. "Now I've got corporals with eight years experience. Our non-commissioned officer corps is as good as it's ever been."

Sergeants major, the highest-ranking enlisted men in the service, are responsible for overseeing training, morale and the material needs of their soldiers. In today's armed forces, they are expected to lead, not shove. For these men, the difference is crystal clear.

"Twenty years ago we were managed, and we didn't like it," said Marine Sgt. Maj. John J. Brown, 43, who served in Vietnam in 1972. "We wanted to be led, not managed or pushed around. We lead today, and we teach. That's what makes us better."

Officers also appreciate this distinction and understand that military leaders today must relate differently to their soldiers. "I think we as officers have grown," said Army Col. Ed Simpson, 47, a two-tour artilleryman in Vietnam who now serves as VII Corps deputy chief of staff. "In a very simplistic sense, we tell our soldiers why. In Vietnam there wasn't a whole lot of that. In Vietnam there was a lot of 'do it.' "

Part of the transition to "why" was dictated by technological necessity. Today's weapons are more elaborate and complex than the hardware of Vietnam. Soldiers today typically spend more hours in classrooms than ever before. "We want them to be versatile, more mature," Brown said. "We want them to ask questions."

The armed forces also have had to come to terms with the diseases of modern society: "Our army has faced up to social conflict," said Simpson. "Our racial problems are almost none because we've focused on them. The leadership has recognized them and deals with them."

And drug abuse, according to the leadership, is a thing of the past. The Marines' Boomer, 52, a veteran of two tours in Vietnam as a company commander and an adviser, recalled with visible dismay the rising drug abuse "in all of the U.S. forces" late in the Vietnam War.

"But today we in essence have a drug-free corps, not only here but back in the states," Boomer said. "One thing that strikes me when you look in their eyes is they're clean-cut kids, if I can use that term affectionately."

Still, the transition has been long, and in some phases difficult. Sgt. Maj. Joseph Cheek, 52, of the Army's VII Corps, recalls the retirement of many experienced sergeants in the latter years of the Vietnam War. "We never got over it," Cheek said. "We had no unit integrity after that group got out."

The 1970s and 1980s were rebuilding years -- getting the draftees out, getting the volunteers in, integrating women in large numbers. But just as important, Cheek said, the Army had to rebuild its corps of non-commissioned officers and give the child-sergeants of Vietnam a chance to grow into their new responsibilities. "The soldier is always about the same," Cheek said, speaking from the wisdom of 34 years in the armed forces. "There's no such thing as a bad soldier. There are bad NCOs."

By the 1980s the Vietnam veterans had created the armed forces they wanted: Well-led, highly trained and ready deliver a knockout blow on the first try.

But at this point, after nearly five months in the Arabian Desert, the soldiers of Desert Shield are in some ways like race horses standing in the gate. They seem ready to run, but the gate has not opened. They are impatient, sometimes skittish. "Nobody nods off in class out here," said the Marines' Brown.

The Marine sergeants major spend hours answering questions about combat: What was it like in Vietnam? How will it feel here? The reason is simple, Sgt. Maj. Kendall said. "Marines aren't dumb. They figure that since you made it through a war, you must know something, and they want to know what it is."

Preparing for the worst is something the Vietnam veterans are well qualified to teach. Cmdr. Sandy Gotch, 45, head surgical nurse at the Navy's Fleet Hospital 5, handled Vietnam casualties at a San Diego Hospital during the 1960s and is readying her staff for "sensory experiences that a lot of them haven't seen before."

"There's going to be a lot of stress, and I need to know when someone's had enough {preparation} so I can get them some time to sit down, get away from it," Gotch said. "Training is the only way I know how to do it. The waiting bothers them, but I keep everybody learning and working. I'm being real hard-line about it. Sometimes they don't appreciate that, but that's their problem."