GENE SIRLOUIS is a no-nonsense grocery shopper. With an arm so quick it could keep pace with a Detroit assembly line, he reaches for groceries scattered on the cement floor, wheels an oversized cart and plans menus at the same time. Christmas is coming, so onto the cart go cans of cherry and apple fillings for pies. Then everyday hard rolls for cheese sandwiches. Cartons of cottage cheese for makeshift lasagna. Pickles to grind up for cheese spread. After the expedition, SirLouis loads his purchases onto a huge scale as the checker tallies the bill. Total: $76.50. Not bad for 779 pounds of food.

Obviously, this no ordinary shopping trip.

SirLouis does not have a huge family to feed, but he does cook for a hungry group. He and the volunteers at the First Congregational and Metropolitan Community Churches serve 40 to 50 homeless women every night. The Capital Area Community Food Bank, the warehouse-sized supply house SirLouis has just visited, provides most of the food.

This area's food bank is one of 43 such groups nationwide that act as middlemen in the food chain. It gathers food donations from manufacturers and retailers (much of which is unsaleable to the general public), stores the food in its northeast Washington warehouse, and sells it to poor and needy groups at 10 cents a pound. Washington's food bank disperses to 210 member agencies that include day care centers, soup kitchens, churches with on-site or emergency feeding programs and half-way houses. They buy a total of 150,000 pounds of food there a month, feeding about 50,000 people -- a small percentage of the city's poverty population. According to the U.S. Census Bureau's 1980 estimates, there are 253,919 poor or near-poor people living in the District.

SirLouis, says Brenda Diggs, agency coordinator for the food bank, "is very, very creative" with the food he buys.

This particular morning's shopping trip is no exception. "Look at these muffins," shouts SirLouis, pointing to english muffins in bins that look like playpens for bread. He steps into a walk-in freezer stacked with yogurt and cottage cheese. He will use the yogurt in muffin or pancake batter; the cottage cheese will be layered with ground meat, macaroni and tomato sauce in SirLouis' famous mock lasagna.

From tables of Giant Food salvage material (Giant and Safeway, in cleaning out their warehouses and stores, give the food bank damaged or outdated food that is unsaleable but not inedible), SirLouis scoops up 10 packages of vanilla pudding which will be topped with sliced bananas for banana cream pies. Then he heads for hard-to-come-by canned items -- mayonnaise, apple juice, grape juice, tomato sauce.

A lot of times, admits Sirlouis, he buys items that he may not have immediate plans for. Vinegar, for instance, could be used in anything from salad dressing to "washing the windows."

After weighing out, SirLouis carts the hand truck, now unwieldy with the load, outside. All 779 pounds of groceries fit into a Datsun -- apparently not an unusual feat for SirLouis. "Gene got 960 pounds of food in a Fiat once," says Sue Curry, a volunteer who helps SirLouis with the shopping.

Since the food bank is not an abundant source for items such as milk, meat and fresh produce, SirLouis depends on dry milk and ground meat that his church receives in donations, and fresh produce from congregation members with overloaded gardens. Serving meat often is not a priority, so SirLouis substitutes with a lot of beans and cheese. He and the volunteers call it "Ronald Reagan cheese."

Among the offerings SirLouis leaves behind are marshmallow cream topping, jars of which are stacked on the floor near scattered bottles of Magic Shell, a chocolate coating for ice cream. Boxes of M&Ms, peanut and plain, are piled in the center of the warehouse. Sometimes, says Curry, the food bank gets "useless stuff. "Food Bank Philosophy

Rick Stack, director of the Capital Area Community Food Bank since its inception three years ago, points to the towering boxes in the food bank's storage area, explaining where the food comes from, and why. "A test market item that didn't fly," he says, referring to two boxcars' worth of Nutri-Grain rye and barley cereal. The boxes of M&Ms the food bank received, Stack speculates, may be due to deterred Halloween sales after the recent Tylenol scare, that left the manufacturer with an excess. Quaker Oats, Stack said, is an especially generous contributor, donating instant grits, cereal and the like. There's grapefruit juice that turned brown (the food bank theorizes that the fruit was frozen on the trees, or that extra oxygen got in during processing), and taco shells that became outdated in a Safeway warehouse. Recently Murry's Steaks donated a load of chicken livers; and Washington Beef has donated freezer-burned meat, which is usable in soups or stews.

Stack admits the food bank's tendency to be overstocked with heavily sugared products like candy bars and marshmallow cream topping as opposed to staples and canned goods. "If I had my druthers, I'd have this place stocked with nothing but peanut butter and tuna." But, says Stack, the food bank doesn't want to deter the goodwill of contributors, who donate food for free. He is also disappointed that some user agencies are too rigid in their thinking. They'll come to the food bank, says Stack, look around, say, "We're having hamburgers. They don't have hamburger buns," and leave, instead of substituting english muffins, for example.

Stack says nutritionists have lambasted the organization for distributing foods low in nutrition, but that they don't understand the food bank's function. Agencies should use the food bank as a supplemental source of food, says Stack, and get what they can for 10 cents a pound. "Then with the savings they can get cottage cheese or eggs or what they don't have" at a regular supermarket. "We're trying to attack hunger by attacking food waste," says Stack. "Anything we can get our hands on is better than going to waste." And, says Stack, there's a "psychological value to a lot of things that don't have nutritional value."

The most difficult task the food bank has is convincing companies to contribute. In addition, many industries recycle what would normally be discarded. The dairy industry may recycle undrinkable milk into cottage cheese, the bread industry turns outdated bread into bread crumbs, the meat people may recycle their discards into dog food.

At Christmas, says Stack, the food bank never gets food proportional to the demand made by agencies, and often the food bank doesn't get special holiday food; "If we're lucky, we get turkeys after Thanksgiving," says Stack.

The usefulness of the food bank shouldn't be overestimated, though, he says; "This a food bank isn't the answer to the Reagan program," as he puts it. It may tide the poor over for a few days, says Stack, but there are other programs that the poor depend on, such as food stamps and the Women, Infants and Children (WIC) program.

Nancy Amidei, of the Food Research and Action Center (FRAC), agrees. "Food pantries and food banks are so literally a Band-Aid," she said, pointing out that food stamps only reach 20 million people, and that the poor and near-poor in the country total 43.8 million. "A real Christmas present for poor people would be to urge Congress to be more generous with food stamps," she said. Cooking Up a Storm

"Something's wrong somewhere when they the government start giving away mozzarella cheese," says SirLouis, as he bustles around the hot church kitchen, overseeing the two volunteers assigned for the evening meal. The menu: carrot and raisin slaw and SirLouis' makeshift lasagna, granola bars, and coffee (Sanka) and tea.

SirLouis' training as a Marriott manager is evident in his organization of the church kitchen. The storage room is piled neatly with rows of canned green beans, beets and potatoes (SirLouis says he's stocking up for next year), as is the freezer with its boxes of ice cream, margarine and Lean Strips (a bacon substitute). A menu calendar and recipe ideas are tacked on a bulletin board.

Preparation is under way for the evening meal: eight pounds of macaroni fill a huge pan, then sauce is spread over all, then a layer of about 12 cartons of cottage cheese, ground meat fried with onions, more sauce, then parmesan cheese. "I've never seen lasagna like this," says Kathy Greene, one of the church volunteers. "It'll be on the menu at the Palm next week," jokes SirLouis.

After cooking in the large oven, SirLouis and the volunteers lug the food to an upstairs classroom where it is served buffet style. The 40 or so homeless women trudge in, some old, many middle-aged, some quite young. At dinner, a few discuss the need for more shelters for women in the district. "Where can a woman sleep safely?" one asks. It's no use going to another city, says another. "It's just like going from one frying pan to another."

Several praise SirLouis and his cooking. "This reverend's good to the poor," comments a 38-year-old homeless woman. Anticipating the holiday spread, she explains excitedly, "They've got so much food here then." In fact, she boasts, "I don't think the president gets what these people get."