They shamble through each stinking alley with the gait of men old before their time, burdened by more than the weight of their kits. The Mesopotamian sun is molten today, again, and they sweat like horses. A room here, a balcony there: They sweep the town in small teams, eyes darting from corner to dim corner.

In a war dominated by armored juggernauts and precision munitions dropped from 20,000 feet, infantrymen are the proverbial boots-on-the-ground. If the dismounted infantry has played a secondary role since the war began on March 20, its stock has risen in recent days as troops have been needed to seize and subdue cities bypassed by tanks and armored personnel carriers bound for Baghdad.

In a pattern repeated in Najaf and Karbala, and which may be a template for the Iraqi capital, armored forces "set the conditions for success by shooting the big pieces, and then the infantry moves in to clean out the die-hards and secure the town," one Army general said.

Ernie Pyle, the legendary war correspondent, called infantrymen the "mud-rain-frost-and-wind boys." He forgot dust. Troops here from the 101st Airborne Division have for weeks been living in a four-inch layer of brown talc that has become a fifth element, along with fire, earth, air and water.

They sleep in burrows, or the back of Humvees, or on the floors of abandoned buildings. A few have tents, which are dust and heat traps. "It's going hot," said Sgt. Todd Swenson, in Najaf with 1st Brigade. He looked parboiled. No one has running water or flush toilets or supper served in anything other than a plastic MRE pouch.

Pyle's description of World War II infantrymen in Tunisia in 1943 remains apt for thousands of Screaming Eagles: "There are none of the little things that make life normal back home. There are no chairs, lights, floors or tables. There isn't any place to set anything or any store to buy things. There are no newspapers, milk, beds, sheets, radiators, beer, ice cream or hot water. . . . A man just sort of exists."

It is not a life for the fainthearted. Most cannot recall when they last showered, other than a vague "early March" or "three weeks ago." Allocated roughly a gallon of water a day, they must drink virtually every drop to avoid heat-related health problems.

They have missed birthdays, anniversaries, vacations, reunions, births, deaths. They will miss many more. Little things are annoying, like cuticles that crack from dehydration and make every reach into a pocket painful. Little things are gratifying, like the 2nd Brigade's discovery in the Kufa Factory for Soft Drink and Healthy Water of endless cases of passable canned orange, apple and lemon-lime juices and cola.

Everything takes longer than it should. Nothing is easy. An immense amount of time is spent rummaging in the dark, looking for stuff in rucksacks or barracks bags; more time is spent in the Sisyphean task of cleaning dust from weapons, glasses, gas masks. The 101st motto -- "Air assault!" -- has been supplemented by the credo of central Iraq: "Embrace the suck."

Food is discussed with epicurean enthusiasm. Is MRE Menu No. 5 -- grilled chicken, minestrone, wheat snack bread, apple jelly, M&Ms, fudge brownie -- really superior to No. 14, pasta with Alfredo sauce, pears, pound cake? It all tastes like cardboard but, at times, is undeniably delectable.

For many, this expeditionary war in Iraq is only the latest campaign in an endless global war.

"In the last 51/2 years the longest I've been home is seven months at a stretch. It's getting old," said Sgt. 1st Class Bill Endsley, who works in the division plans cell. "I have a 6-year-old and an 8-year-old. They still call me daddy, so I guess they know who I am.

"It's interesting to watch the conversations evolve over here," Endsley added. "When the soldiers first leave home, it's about all the things they want most when they're at home: [women], a beer. Then, when they've been here a while, it's about a shower, or a bed, or wondering what it's like not to wear the same uniform for a month."

Still, there is a strange beauty in the austerity: the bowl of stars on a moonless night; the glow of orange chemical sticks, like Civil War campfire embers; the love of comrades that blooms on battlefields. If too terrible to be romanticized -- men and women die, suffer and kill daily -- the infantry can claim a rugged nobility that Pyle sensed in observing that "the velvet is all gone from living."

"There is no greater commitment than that which is made by putting the American infantryman on the ground," the division commander, Maj. Gen. David H. Petraeus, told a rifle company while awarding two Purple Hearts in Najaf last week. "You've really walked point for our nation in this particular battle and this part of the campaign. You've performed brilliantly in countless ambiguous situations."

A hundred infantrymen came to attention, then picked up their weapons and returned to the fight.