WITH U.S. FORCES, SAUDI ARABIA, DEC. 3 -- In her unit's command trailer, such as it is, Army Sgt. Molly Diskerud of the 351st AG Company is taping up decorations sent by the Forest Park, Ga., middle school, simple messages scrawled by junior high school kids on cutout Christmas trees and snowmen:

"We hope that you have a Merry Christmas, and keep up the good work," read one inscription. "God bless you, we will be thinking of you."

It is mail for the mailman. The 351st, a postal reserve company and the pride of Tallahassee, Fla., is the unit in charge of receiving and distributing hundreds of tons of letters and packages that arrive in Saudi Arabia daily, destined for the Army soldiers of Operation Desert Shield.

At this juncture, with diminished prospects for immediate combat and with Christmas coming on, the 351st knows there is no more important job in the U.S. armed forces right now. The arithmetic speaks for itself:

"When we first got here {on Oct. 9}, we were sending out 20,000 pounds of mail a day," said Diskerud, 29, a mail dispatcher who was a payroll clerk in Tallahassee before the company was called up. "Within a week we were up to 40,000 pounds, and within three weeks we were doing 325,000 pounds."

Sunday, the 351st, helped by volunteers from other Army Reserve and National Guard units from other parts of the country, handled 586,000 pounds -- 293 tons -- of letters and packages. "They're saying we could get up to 800,000 pounds a day," said Capt. Stan Richeson, the 351st's company commander. "It's been growing steadily, and it keeps tracking up."

Army officers here are at a loss to explain the quantity of mail, which, according to most accounts, is far above the volume received by soldiers during the Vietnam War, the last time the Army had a Desert Shield-sized force deployed in a foreign country.

In any case, civic organizations, towns and schools like the junior high in Forest Park, have adopted infantry companies, National Guard detachments and even individuals. Richeson said he is the regular -- and grateful -- recipient of newspaper clippings, sports scores and letters sent to him by three people he didn't even know before he came to Saudi Arabia. "This happens to all kinds of people," he said. "We wonder where they get our names."

Desert Shield's postal system seems simple on its face. Mail arrives seven days a week aboard military cargo aircraft and civilian charters. It is packed in 600-pound cardboard boxes, each labeled with one of seven Army Post Office (APO) numbers currently in use for Desert Shield. Navy, Marine Corps and Air Force mail is handled separately by those services.

Flatbed trucks bring the boxes to the 351st's mail depot, where they are unloaded, shuffled according to APO and put aboard another set of seven trucks, each labeled with a different APO number. Loaded trucks leave for the desert, to be replaced immediately by empties. The process, it seems, is eternal. The 351st and its friends -- about 150 men and women altogether -- work day and night in two 12-hour shifts, seven days a week.

The 351st opened for business in a 6,000-square-foot shed, where Richeson said it was "lucky to move 80,000 pounds a day." At a second site, the company pushed its daily volume up to 300,000 pounds, "but we were standing knee-deep in sand," Richeson said.

The current "facility," Richeson and others believe, has solved the problem. It is nothing more than a large expanse of new blacktop with a loading dock smack in the middle. Diskerud's trailer, parked to one side, is the office. The depot is stark, utilitarian and ugly, like a New Jersey Turnpike rest stop stuck in the middle of the desert without a diner.

But it does the job -- or its share of it. Richeson says mail takes about 48 hours to reach Saudi Arabia. His crews sort it, pack it and move it out in another 48 hours. He doesn't know how long a letter waits in the United States before it is put on an airplane, nor does he know how long each APO needs for sorting before the mail is delivered to individual soldiers. Letters from his own wife and three children arrive from Tallahassee in "10 days to two weeks."

Bizarre circumstances often complicate the mailmen's job. The Secret Service commandeered truckloads of the 351st's mail to use as a barricade to screen President Bush when he arrived for Thanksgiving with the troops. This reportedly put a knot in the mail pipeline that still causes delays.

But the company's biggest headache is mail intended for a specific soldier that bears no APO number, only the soldier's name and the number "848," which is the code for "Any U.S. Serviceman." The 848 mail -- about 3 percent of the total -- is distributed to lonely soldiers who aren't getting letters. But, he added, "848 is useless in locating a specific soldier." Instead, the soldier must be traced by computer, a task he says can delay delivery several days.

One current sinner, Richeson said, is a New York department store that has run a promotion whereby, for a charge, it sends a "care package" containing games, a T-shirt, a teddy bear, candy and other stocking-stuffer gifts to loved ones in Desert Shield. Unfortunately, he said, they are arriving in Saudi Arabia -- at the rate of 10 to 20 a day -- inscribed with only the soldier's name, social security number and the 848 code.

Still, if enthusiasm were all that was required, every serviceman and woman would have letters and presents well before Christmas. Maj. Willie Newson, the Regular Army officer in charge of the Army's mail, calls the 351st and its volunteer friends "unbelievable. These people work so hard, we couldn't survive without them."

This may be due to the unusual cohesion of some Reserve and National Guard units whose members have met for years on weekends and in summer camp, and have now embraced the chance to serve on active duty.

"We've all been together four to five years, sometimes longer," said Sgt. Lewis Rafter, 36, of the 1122d Transportation Co., National Guard truck drivers from Monticello, Ark., who volunteered to fill in as postal clerks. "We're like family."

"Put it this way," added Spec. 4 Cornell Harris, 20: "This unit is just about the best unit out of Arkansas."