Although you don't see much of it on those upbeat "Be all that you can be" television commercials, the U.S. Army is fast acquiring a new image.

American combat-ready soldiers massed in review at Fort Ord, Calif., or spread in squad formations across fields in West Germany, or preparing to hurtle from aircraft in parachute maneuvers at Fort Bragg, N.C., no longer look like cartoonist Bill Mauldin's prototypical "Willie" and "Joe" of World War II, or the GI footsloggers in Korea or the kids afflicted with the thousand-mile stare in Vietnam.

What they do look like is a matter of some dispute, but the reason for the change is not: The troops of the volunteer Army, and the U.S. Marines, and Army Reserve and National Guard units across the land are being equipped with what researchers and bureaucrats call PASGT (pronounced pass-get), an acronym for Personnel Armor System for Ground Troops, the key elements of which are a ballistics protective vest and, above all, a new, molded, laminated Kevlar helmet.

The old M1 helmet, the "steel pot" born of necessity in the early days of World War II, is going, going and, quite soon, will be gone.

"This is absolutely the best helmet in the world today," engineer Philip Durand states unequivocally. "I guarantee if we show anybody what we did and why we did it, he will say, 'What a beautiful helmet.' "

Durand is half of the team largely responsible for the new design. Lawrence McManus is the other half. They work at the Armor and Special Projects Branch of the Individual Protection Laboratory at the U.S. Army Research and Development Center in Natick, Mass., and between them, they estimate, they have accumulated more than 50 years of helmet research.

"We thought it out without any preconceived ideas," Durand adds. "It wasn't an artist's concept. It wasn't just something a general or two happened to like. It was a very logical, sequential, step-by-step, cause-and-effect development."

"Hey, we thought it looked like a Little League baseball cap," quips McManus.

Like Little League baseball caps and, more potently, like German helmets from World War II, the silhouette of the new American combat headgear shows a pronounced dip from the edge of the visor to the line of the ear and neck. To many Americans inside and outside the Army this image conjures old hostilities and fears. It is the "Nazi helmet," the essence of Evil and Enemy. By contrast, the steel pot represents Good and Country. And, as the new foot soldiers know all too well, you can't cook in the new helmet, and you can't shave out of it, either.

These factors, and the cost -- $87 per unit compared with about $30 for the M1 helmet and liner -- explain the lengthy delay in getting the PASGT helmet to the troops. Voluminous, painstaking research, initially intended simply to improve the steel pot, began in 1968. The design of the new helmet was fundamentally complete by 1974. Worldwide testing of the product was finished by 1977. Approval from the Joint Chiefs of Staff was granted in 1978. Yet procurement and distribution just inched along.

"I had difficulty getting it into the system because of the visual perception of it," recalls Vivian McKenzie, acting project manager for the Clothing and Individual Equipment Command of the Army Materiel Command in Alexandria, who was in charge of the initial distributions. But, she says, "the Grenada incident did it."

As part of the Army's Rapid Deployment Force, troops of the 82nd Airborne Division at Fort Bragg were the first to receive the PASGT helmets. Consequently, they were the first to wear the new issue on a combat mission, when President Reagan dispatched U.S. units to Grenada in the fall of 1983. Many Americans got their first view of the helmet in television and newspaper images of that operation, and the response perhaps prompted the Pentagon's low-key approach to any further publicity.

But the performance of the new equipment surpassed expectations. In two well-documented examples, the helmets stopped a vicious bevy of fragments from a 20 mm missile and a round fired from a Russian AK47 rifle. Although even the new helmet is not designed to protect its wearer from direct rifle rounds -- "stopping that AK47 bullet was luck, like a Doug Flutie Hail Mary pass," McManus says -- response was alacritous throughout the armed forces. Shortly thereafter, the Marine Corps, which until then had disdained the new helmet, put in its order.

Today, McKenzie says, distribution is proceeding rapidly, and by 1988, nearly 2 million PASGT helmets will be in use.

So the next time you see massed troops wearing steel pots on television or in the papers, they probably won't be Americans. They very well could be Germans, though. Soldiers in the Bundeswehr have been wearing a version of the M1 helmet ever since the West German army was reconstituted in 1956.

The question is, did the Germans know something we didn't back in World War II? Was their helmet intrinsically superior to the steel pot?

"No, their design just came about from an artist's concept," Durand says derisively. "In fact, in terms of ballistics it wasn't nearly as good as the M1. It was too close to the head and it had a terrible suspension system with a lot of metal components inside that became secondary missiles."

What about the broad, angled "skirt" around the German helmet? Didn't it offer more protection than the steel pot, with its narrow rim?

"No," Durand says. "That was a leftover from World War I, from trench warfare, when the soldier was in danger from being hit by falling rocks and debris from explosions. That's why the British 'pie plate,' the one we were using in Bataan, had the skirt."

Well, if the old German helmet was so bad, why does the new American helmet look so much like it?

"Actually, it doesn't, if you look closely," McManus says, and he's right, up to a point. The American helmet seems to fit the head better, it has a molded protrusion for the ears, and it lacks the distinguishing flare of the "skirt." Even so, anyone with strong memories of World War II isn't likely to be so analytical.

The only positive aspects McManus and Durand see in the old German helmet are that "it was stable, because it sat lower on the head, and it provided peripheral vision." Those are but two of the many advantages that the pair see in the new American helmet.

"The philosophy of this program began with the obvious assumption that to attain maximum protection to the head one should cover the entire head," states a 1976 Army report, "Development of a New Infantry Helmet."

Common sense dictated that this medieval ideal was not suitable for the 20th-century infantryman. But McManus, Durand and their colleagues in various Army research organizations, setting out to design the first new U.S. helmet since World War II, were leaving nothing to chance.

"Every design aspect reducing the ideal coverage was documented by a corresponding study recommending such a cut or standoff," states the 1976 report. Thirty-two studies were conducted, involving everything from the sizes and shapes of human heads to ballistic material evaluation. The tests produced three U.S. patents, praise from the National Academy of Sciences and, not exactly presto, the PASGT helmet.

Sizing was a particularly nettlesome issue. The problem, say McManus and Durand, was that conventional data on the human head, including information the Army acquired by measuring the heads of 6,600 soldiers, does not take into consideration the vagaries of individual head shapes. "Sizes just don't go up from 7 1/2 to 7 5/8 and so on," Durand says. "It's like a Miss America contest where the perfect measurements are 36-24-35 -- not one of those women will have all three of those measurements."

After several laborious false starts, McManus and Durand devised a "3-D numerical surface descriptor," a transparent hemisphere fitting over the head and equipped with needlelike probes to measure distance from the head at 27 points. The thing looks like an instrument of torture, but it provided the researchers with the information they needed -- that is, it gave them three-dimensional data concerning head shapes corresponding to the voluminous two-dimensional measurements.

"In our eyes the heads actually were more important than the helmet," Durand recalls. "They became the basis from which we designed. The ideal helmet from the ballistic point of view would be a bathing cap, because it moves with the head and thus gives the greatest possible stability, and it presents the smallest target."

The sizing effort was characterized as "the most comprehensive anthropomorphic data-gathering program ever established for the head" by the National Academy of Sciences, and the awful-looking apparatus won McManus and Durand one of those three patents. As a result of this work, the new helmet, which comes in four sizes, fits much better than did the steel pot, and thereby helps to answer the three primary complaints from the field regarding the old helmet -- stability, fit and comfort.

Concurrent tests were conducted on ventilation, one of them using a full-scale "copper man" to measure insulation values and "vapor transmission coefficients of clothing systems," and on "transient deformation" -- "the distance a given material will momentarily deflect when impacted by a missile of known mass fired at non-penetrating velocity," or what a soldier might call a helmet's headache potential.

In other words, a hard bathing cap would be hot, uncomfortable, and would transmit an awful headache to its wearer when hit by anything larger than a small pebble. These tests proved that a one-half-inch standoff for the head was adequate for ventilation and transient deformation in a helmet using Kevlar, the tough new polymer developed by Du Pont originally to replace steel belts in radial tires but whose chemical properties make it ideal for ballistics protection. (Kevlar is also used in the PASGT vest.)

At this point the researchers basically had the inside of the helmet designed. The information was passed on to a sculptor who prepared working molds, and tests continued concerning the exterior properties of the helmet -- what shape would provide the optimum mix of visibility, hearing, weapons compatibility and protection -- and on the suspension system.

When a prototype based on criteria established in these tests was first field-tested in 1974 at Aberdeen, Md., it received, according to Durand and McManus, the "highest level of troop acceptability of any item of clothing in Army history."

A surprising result of these tests, in view of the fact that a prime complaint about the steel pot was its heaviness, was that the new helmet was perceived as being lighter than the M1, even though its actual weight was about the same.

Why? "The center of gravity is lower, it's closer to the head and it just fits better all around," McManus says.

The result is a helmet with a built-in, adjustable suspension band and an outer shell made of 19 laminated layers of Kevlar. It covers 11 percent more of the head than the M1, provides better visibility and greatly increases stability and comfort. Most importantly, it increases protection. "It takes 2 1/2 times the energy to penetrate this helmet as it does the M1," Durand states. "We can expect head casualties to be reduced by 25 to 30 percent in a given scenario" with the new helmet.

In addition, there are intangible advantages. In the first field tests, 11 years ago, soldiers equipped with the M1 and PASGT helmets ran parallel lines along obstacle courses. "The soldiers invariably took off the steel pot when they were done with the course," Durand recalls, "but many would just leave the PASGT helmet on. We knew we had a comfortable helmet then." In Vietnam quite a few casualties resulted from hits taken on helmetless heads. This is not likely to happen with the new helmet.

Of course, a trooper can't cook in it or use it as an instant early morning wash basin. "You can't cook in it, but you won't bleed in it either, is what we tell the soldiers," concludes McManus.

The new helmet is, in short, a classic example of the design dictum that form follows function. Its great beauty is that it saves lives.