For 12 years Eric Nattrass has been a good soldier, patiently enduring the Army life: the orders to shine his shoes until he could see his reflection in them, the bivouacs in the mud and cold rain, the tours in Vietnam, the unpaid overtime and what he calls "the silly bickering and constant bureaucracy."

Now the service may have pushed this husky sergeant over the limit.

At 32, and with 215 pounds on his 6-foot-1 frame, Nattrass is on the verge of quitting. The reason: He's been declared 12 pounds overweight and ordered by his commanding officer to eat a mandatory diet of steamed rice and fruit Jell-O at the mess hall until he gets down to fighting trim.

"I'm not being treated like a man," the veteran soldier grouses.

"In time of war we need physically fit people," counters Col. James C. Blewster, 50, the slightly paunch commander of the 3,500-member Transportation School Brigade who developed the program. Dubbed "Lifestyle '81," the project is believed to be the first such mandatory diet program in the military.

Along with 49 other overweight soldiers here at Fort Eustis, a bleak, sprawling post 180 miles southeast of Washington, Nattrass has been placed on a 1,500-calorie-per-day diet. He also has been relieved of his $122 monthly food allowance and ordered to eat every meal in a specially supervised mess hall here for the next 10 weeks.

"Even though I'm only eight years from retirement, I'm seriously considering leaving the Army because of this," the normally soft-spoken Nattrass fumes. "I'm not being treated like a man. The Army doesn't care that I'm dedicated; they'd rather worry about a trivial little thing like this."

But officials say being overweight and out of shape is scarcely trivial, especially at a post such as Eustis that has a large percentage of senior non-commissioned officers with sedentary desk jobs.

The Army can deny promotions, discharge soldiers for "apathy" or bar the reenlistment of those deemed too fat, but such proscriptions have been exercised only rarely.

Officials here have not said what will happen to soldiers who do not lose the requisite one or two pounds per week. According to Blewster, the success of the program will be evaluated at the end of 10 weeks.

"We're not trying to be hard-asses," said Maj. Eric Lunde, Blewster's assistant, who resembles a trim, reddish-haired Errol Flynn and wears a camouflage print scarf knotted around his neck.

"Half of these guys haven't figured out that we're doing this for their own benefit because being overweight is just plain unhealthy. We found that half of these people had high blood pressure and only one knew it."

The unusual program, which includes three mandatory exercise sessions each week, has attracted much public attention, a circumstance that has pleased the brass while infuriating some participants. One enlisted man, who preferred anonymity, branded it a "total display of authority and a stupid publicity stunt by a colonel who just wants to make general."

Some soldiers applaud the aims of the program and agree that the food is good, but said they resent the fact that TV cameras were present as they weighed in. The resulting broadcasts featured close-up shots of beer bellies and multiple chins. Others resent being absent from home at mealtime and explain that they depend on their monthly food allowance in preparing a family budget.

"We're the new American hostages," complained Sgt. Charles J. Gargulis, 39, as one TV crew followed a group of embarrassed, fatigue-clad GIs along the cafeteria line in Echo Company's mess hall, renamed "Lifestyle Inn." The camera recorded the sight of cooks carefully weighing three-ounce portions of ham on tiny diet scales.

"Even though the chow is super, this is absolutely the most degrading, worst-managed program I've ever seen in my 19 years in the Army," said Gargulis, a maintenance supervisor, who has been told he must shed 45 pounds from his 6-foot-1 inch body.

"I cannot understand why it was okay for me to go train crews in Vietnam weighting 315 pounds and get shot at, but now that I've got a desk job and I weigh 250 I'm too fat," he said, stabbing a forkful of lettuce covered with "no-cal" dressing into his mouth.

"It's not like being an alcoholic or addict, I don't pick up the phone and say, 'I can't come to work, I'm too fat," said Nattrass, who added that his excess weight does not affect his ability to write training manuals. "Besides, I lost 57 pounds in Germany by myself without any harassment from the Army.

"This program is disrupting my whole family life," he continued. "The only time I used to see my wife was at meals because she works nights and goes to school. She called me today at work and asked if she could make an appointment to see me."

Sgt. Marvin Livingston, 36, has been told he must lose 40 pounds to meet Army weight standards, which are based on life insurance actuarial tables.

"Now I never see the kids [age 13 and 14] and my wife is so mad she's on fire," he said. "I think the program's a terrific idea but it's going to cost me $140 this weekend for my wife to buy firewood because I won't be home to chop it. I don't think they should mess with people's weekends."

Army officials attribute much of the criticism to the grousing of malcontents and say that they are trying to minimize any hardships the program may have created. Blewster says that soldiers' families will, for the program's duration, be allowed to pay to eat in the mess hall, which has been redecorated with plants and pictures and outfitted with lots of full-length mirrors.

"I look at this program as one of loyalty -- loyalty from the top down," says Blewster, who recently told his troops he sympathized with their problem because he was once "the kid they called Fatso." Blewster says he vanquished the enemy -- fat -- 19 years ago through a combination of willpower and change of life style."

The colonel, who has declared the post snack bars off-limits, has archly reminded the soldiers that successfully participating in his program is "far less expensive or inconvenient than being forced out of the Army to reestablish yourself in some new line of work."

Sgt. Wayne Damba, an enthusiastic supporter of the diet program, agrees. "This is the most concern the Army's ever shown for me," he says, lighting a cigarette after a low-calorie lunch of pork and mashed potatoes.

Damba's 29-year-old wife, Carlena, who works as a secretary at the post, says she plans to join him in the mess hall for every meal. "One reason me and Wayne are in this shape is we didn't learn to eat right," she says, adding that she grew up in the mountains of Southwest Virginia and "ate lots of filler like cornbread and pinto beans. I think this program will reeducate us."

That's precisely what Blewster hopes.

"There's no social stigma to being overweight on the outside at all," says the 5-foot-10 officer, who weighs 183, a full 11 pounds under the maximum allowed by Army regulations. "I think if people participate eagerly in this program, the day will come when they'll be extremely grateful."