WITH U.S. FORCES, SAUDI ARABIA -- For Marine Cpl. John B. Smith, home is an open tent on a sun-baked concrete dock. Some mornings he is jolted awake by a helicopter landing a few yards away, its rotor blades driving a stinging spray of sand through the tent.

The highlight of his long, hot day as a military policeman is the arrvial every evening of the big orange mail sack bearing family news from mom in Austin, Tex., the latest sports scores from grandma and scribbled notes from his little sister.

"It's the best part of the day," said Smith. "It's the one thing we have to look forward to out here."

As it has been for centuries for troops far from home, mail call has become the spiritual lifeblood of U.S. forces assigned to this grim desert environment. It is their single tangible link to the familiar in a land where nothing is familiar.

Letters from home are so critical to morale here that military postal units give bundles of anonymous "Any Serviceman" letters written by school children and nursing-home residents to every chaplain for distribution to lonely, depressed soldiers who may be receiving little or no mail.

"It's like being Santa Claus every day," said Lt. Lori Fanning, 22, of Columbia, S.C., who serves in one of the military postal units here and frequently acts as a letter carrier on one of the many desert mail routes. "People are always happy to see you coming."

More than five tons of mail for U.S. military personnel has poured into the Middle East since Operation Desert Shield began more than a month ago, and officials here expect that amount to multiply rapidly in coming weeks as more troops arrive and the distribution process becomes smoother.

A giant Persian Gulf-region military postal facility is being readied on Long Island, and Air Force Maj. Michael H. Whitaker, the service equivalent of a postmaster general around here, said he has requested extra transport planes and helicopters for the Christmas season.

All packages sent here are subject to strict Saudi customs, however, and one GI, at least, will not be getting his parcel of Jack Daniels, vodka and magazines featuring photos of scantily clad women. Every incoming videotape is viewed for violence or obscene material. Religious items also are forbidden.

But some suggestive material does reach the tents and trenches, nevertheless. From the top of a nearby stack, Fanning plucks a letter addressed: "To a Lonely Serviceman" -- with "man" underlined. The sender: "A Single School Teacher from Georgia."

"People are already hunting husbands out here," said Fanning with a grin.

When they're not devouring letters from home, the threat of imminent combat does a lot to shape the reading habits of U.S. forces here, from top-ranked generals to the grunts in the field.

Lt. Gen. Walter E. Boomer, commander of all Marine Corps units here, read pages from Omar Bradley's "A Soldier's Story" during his first nights in Saudi Arabia. He has since moved on to a thick volume of Saudi Arabian history.

Col. Jesse Johnson, recently shifted from U.S. special forces in Europe to heading up special operations here, has attached himself to a set of earphones and a thin red booklet entitled "Learn Arabic Yourself."

For the troops spread thinly across the Saudi desert, the Army Intelligence Agency has just rushed into print a small handbook titled, "Identifying the Iraqi Threat and How They Fight." It includes diagrams of Iraqi tank tactics and drawings of their fighter planes.

The handbook comes complete with pronunciation guides to a few crucial Arabic phrases, such as "Hands up!" "You are a prisoner," and "armored personnel carrier." One chapter -- "Poisonous Animals" -- begins with the admonition: "If it moves, don't touch it." It goes on to detail the traits of such hostile reptiles as the horned desert viper, the Egyptian cobra and the puff adder.

The warnings didn't prevent one Army communications team from constucting a small cage to enclose its new pet scorpion. Medical authorities later confiscated it for use in show-and-tell safety lectures.

Enter the canvas abode of British Capt. Giles Orpen-Smellie and you forget for a few moments that you haven't had a shower or a hot meal in four days or that you live in a barren desert rock quarry foresaken by all living things except soldiers, snakes and scorpions. Here a chap can be served a proper cup of tea -- pardon the powdered milk -- and perhaps a tin of curried chicken.

Orpen-Smellie is a British paratrooper ("parachutist," he says) who just happened to be taking part in a military exchange program with the U.S. Army's 82nd Airborne Division when it was ordered to Saudi Arabia.

His tent has quickly become known for its touch of British civility. He and the three American officers who share his quarters begin their day by passing around a metal cup of hot tea and end it with the chef's dinner special.

Not content to spoon out globs of mystery meat from the brown plastic wrappers of military-issue MRE ("Meals Ready to Eat"), Orpen-Smellie -- like many of his American counterparts -- heats his rations over the tent stove, stirring in a touch of curry or perhaps a pinch of chili powder. "Dinner is served, lads."

When the Army dispatched its jungle-green tanks, trucks and jeeps to a dusty desert devoid of any hint of green, soldiers didn't wait for the arrival of sand-colored camouflage paint. Within hours of touch-down, most of the green war machines were given a thick coat of desert mud, which dries to a gritty cream color.

Some troops have honed their camouflaging skill to a fine art, and you won't catch them using just any old sand. Maj. Hank Keirsey, executive officer of an 82nd Airborne infantry unit, declared: "You have to dig down four feet -- that's where the best mud is."Air Force crews operating an air-defense missile battery here decided early on that catching a bus every four days for a 30-minute ride to the showers just wasn't going to cut it.

Now they have the luxury of standing under the drip of a five-gallon water can, with artfully hung ponchos for a shower curtain.

The line for the shower bus is as long as ever.

"Don't get us started," begged one soldier, taking a break from training on a 105mm howitzer. But get them started, ask them what they miss most, what they dream about while sweating in their desert tents at night, and you find their needs are simple.

"A double cheeseburger," declared a Californian. "Just give me a double cheeseburger, and I could take all of this."

"No, no -- Taco Bell," shouted another GI. "A Philly steak-and-cheese," yelled a Philadelphian. "Green grass and birds," said a rifleman from Spokane, wistfully. "A shower you can stand under as long as you want," said his buddy.

And what does Sgt. Albert Valentine, 27, of Washington, D.C., miss? "My two kids. My woman. My dogs. My yard." He paused, and a wide grin creased his face. "I miss my toilet. When I get back I'm going to kiss the porcelain."