Go on, admit it. You've bought your kids Lunchables, those build-your-own meals in the yellow boxes that parents either love to hate or hate to love.

Nate Spiller's wife won't admit it--at least publicly. But he will.

"They really look awful," says Spiller, a Kensington father of two. Still, he gives them to his son Evan, 8, usually twice a week. "It's for convenience. When I'm lazy," he says.

Few like Spiller may own up to it, but he's one of many time-pressed parents looking for an easy out. Just look at the numbers: Oscar Mayer, maker of Lunchables, has sold 1.6 billion of the open-and-eat boxes since they were introduced in 1988. The runaway market leader in the "lunch combination" category, the company has seen a 15 percent increase in sales each year, which totaled about $530 million in 1998.

The first Lunchables were simple packages of meat, cheese and crackers; now there are the best-selling Pizza Swirls and Pizza Dunks, plus hot dogs, hamburgers, tacos and nachos, many of which come with sugary fruit drinks and candy. Waffles and pancakes, complete with frosting packets and syrup, were rolled out this summer, and meals with X- and O-shaped nacho chips will be introduced later this fall. The line also gives Kraft Foods--which owns Oscar Mayer and 70 other brands--another outlet for its many products, including Capri Sun drinks, Tang, Jell-O and Tombstone pizza sauce, not to mention Kraft cheeses and Oscar Mayer meats.

One need not be a cynic to get the gimmick: Provide busy parents with an instant "home-packed" lunch, even if it costs up to $1 more than the school lunch and probably far more than a brown bag one. (The average school lunch costs about $1.55; Lunchable Fun Packs with a drink and dessert cost $2.59.) Give kids their favorite "fun" foods in colorful mini-sized packets that they can open and assemble themselves. Decorate the back of the box with games, contest come-ons, and yes, even Pokemon cards! The combination hits every hot button.

Not surprisingly, Lunchables are also hitting the hot buttons of some nutritionists, educators and parents.

"It's not rocket science to know that sugar, white flour, cheese and meat is not the healthiest lunch to serve your child," says Bonnie Liebman, director of nutrition for the Center for Science in the Public Interest, a consumer advocacy group.

They're "my big bugaboo," says Susan Landmann, a preschool teacher at the Murch School in the District, who says she has sent disparaging notes home to parents who pack them.

"I let them buy one Lunchables a year," says a Bethesda mother, referring to each of her two children. "They bought it on a Saturday, then ate it Sunday. I wrote on the calendar: LAST LUNCHABLES OF THE CENTURY!"

Still, while it's easy to draw a visceral conclusion about a pre-fab lunch of cracker-sized pizza "crusts," cold tomato sauce and squeezable cheese--how do Lunchables stack up in the nutritional scheme of things? How do they compare with the brown bag lunch you might make yourself? Are they better or worse than what your child would buy at school? In other words, what's really in these things?

Ask some nutritionists and they'll likely tell you that one of the major problems with Lunchables is what's not in them.

"They're not really a complete meal," says Mindy Hermann, a nutrition consultant and mother of 9-year-old twin boys. "They're clearly short in fruit, vegetables and dairy. . . all the things kids aren't eating enough of anyway."

The U.S. government recommends that elementary-school-age children get five to nine servings of fruits and vegetables a day. According to the Department of Agriculture, kids ages 6 to 11--the Lunchables target audience--are eating only 3.8 servings. And 40 percent of the vegetables are potatoes, most likely French fries. So if kids don't get any produce at lunch, "you've just missed a big opportunity," says Liebman.

Kathleen Zelman, an Atlanta dietitian and mother of two, says she has packed her kids Lunchables--after scrutinizing the nutrition labels and adding what they lack. Zelman says she buys the smaller packages with lean meat, cheese and crackers, rather than the Fun Packs, which come with candy and drinks containing 10 percent fruit juice. Then, she throws in an apple or some carrot sticks, and her kids buy milk at school. "It's a perfectly nutritious meal," she says.

Indeed, says Claire Regan, spokeswoman for Oscar Mayer, "we do have a variety of choices . . . and we do have low-fat and reduced-fat" versions. And with the regular Lunchables--not the Fun Packs--parents can "customize" with their own drinks or dessert, she added.

But do they? "I don't see them supplementing Lunchables with milk or juice," says Penny McConnell, director of food service for the Fairfax County schools, who feels strongly that the boxed lunches don't deliver "the nutrition bang for the buck." Still, the few times Marie Martin, of Chevy Chase, has given her 10-year-old daughter, Elizabeth Biddle, carrots or apples with her pizza Lunchables, "they came back with the box."

While all Lunchables are not created equal, many of them share common nutritional pitfalls: With no fruits, vegetables or whole grains, they're all very low in fiber. Nor are they particularly good sources of Vitamins A and C. The amount of saturated fat--the kind that can clog arteries--"is not good news," says Hermann. Neither is the amount of sodium, which hovers near 50 percent of the recommended daily intake in several of the varieties.

Because the portions are small, they're not particularly high in calories--many of the Fun Packs have under 500. (Although they are what is called "calorie dense"--a lot of calories for the amount of food you get.) And as for the amount of total fat--on average, it's not bad--many contain less than a third of the recommended daily intake.

In other words, Lunchables won't get stellar nutritional grades. But they're not going to flunk, either.

For that matter, many brown bag lunches need improvement.

Kathy Lazor, food service director for the Montgomery County schools, says that one trend that distresses her is that more and more elementary school children are bringing soft drinks with their home-packed lunches. Or the beverage is a juice box that's not 100 percent juice. There's "usually no fruit," says Lazor, adding that she's not seeing "a whole lot of carrot sticks," either.

Similarly, an April analysis of home-packed elementary school lunches conducted by a dietetic intern for the Fairfax County schools found that none of them contained fruits or vegetables. Although the sample size was very small--only five lunches (including one Lunchables)--it was illustrative of the foods being brought from home. A typical lunch, for example, consisted of a ham and cheese sandwich on white bread with mayonnaise, a bag of pretzels, a six-pack of cheese and peanut butter crackers and a Capri Sun drink.

So how did the Lunchables, a ham and cheese one, compare with that brown bag version? Because the portion sizes were probably a lot smaller, the Lunchables had a lot fewer calories and less sodium and fat. But the comparison shows that if you pack that brown bag with lots of snacks or sweets, a fruit-flavored drink and no fruits or vegetables, you're no better off than with a Lunchables; in fact, it could be worse.

The real purpose of the Fairfax County analysis was to compare the nutrients provided by home-packed lunches (including the ham-and-cheese Lunchables) and the school lunch. Not surprisingly, the dietitian who conducted the survey concluded that most lunches brought from home are less nutritious than school lunches. Over the course of a week, school lunches are required by federal law to contain no more than 30 percent of calories from fat and less than 10 percent from saturated fat. School meals must also provide one-third of the Recommended Daily Allowance of protein, Vitamin A, Vitamin C, iron, calcium and calories.

So at least with the school lunch, there are certain standards. What this means, says nutritionist Hermann, is school lunches are likely to be higher in calcium, fiber and vitamins than Lunchables. And school lunches also have more calories, which active kids may actually need, she added. Indeed a comparison between a Montgomery County school pizza lunch (cheese pizza, carrots with dip, orange, cookie and milk) and a Lunchables Pizza Dunk Fun Pack (breadsticks with cheese and pizza sauce, a Nestle crunch bar and a Capri Sun drink) showed that the school lunch had three times as much calcium, nine times the Vitamin C and almost twice as much fiber.

When developing Lunchables, Oscar Mayer didn't follow any particular nutrition guidelines, says Regan, the spokeswoman. The purpose of the product is to "provide a convenient way for busy moms to occasionally treat their kids to their favorite foods," she said. "They aren't designed to be eaten every day of the week, just as you wouldn't expect an adult to eat a steak dinner every night."

But Landmann, the preschool teacher at Murch, says she has taught children who did bring Lunchables every day. A lot of parents, says Landmann, "give in to kids because it's easier than saying 'no.' "

So is it ever okay to say "yes" to Lunchables?"

"If it's something your child really likes, put a limit on how often he or she can have it," Hermann says. Maybe make Wednesdays Lunchables Day, she suggested, then pack a healthier lunch the rest of the week, or have them buy the school lunch a couple of times.

"There are ways to work around it," says Hermann, "because if you say 'absolutely not,' they'll become the forbidden fruit."

BOX LUNCH ANALYSIS

Here I was thinking that the lunches I packed my son had to be far more nutritious than Lunchables. Until, that is, the contents of a typical Lunchable were analyzed by a computer nutrition program.

His lunch--peanut butter and jelly on whole wheat bread, two chocolate chip cookies, 10 grapes and calcium-fortified apple juice--ended up having more calories and fat and less calcium than many of the Lunchables Fun Packs. (My home-packed lunch did, however, have a lot less sodium and a lot more fiber. And it was also more food.)

Still, I asked Barbara Pearl, an Illinois nutritionist and co-author of "Brown Bag Success: Making Healthy Lunches Your Kids Won't Trade" (John Wiley & Sons, 1997), to make it better.

Her suggestions included using low-fat peanut butter or less of the regular kind, adding bananas or shredded apples to the sandwich, putting in 15 grapes instead of 10, and dumping the apple juice for water or milk.

As for other ways parents can improve their kids' brown bag lunches, Pearl said:

* Keep it simple. A sandwich, a piece of fruit, a couple of cookies, something crunchy like pretzels or crackers and water or milk--even chocolate milk.

* Even if your child will eat only the same sandwich every day, vary the foods that go with it or the type of bread. If your child insists on a bologna sandwich, throw in some carrot sticks or an apple, or put the bologna on wheat bread, wheat pita or crackers.

* Forget the sandwich. Make a shish kebab out of chunks of cheese, lean meat and fruits or vegetables. Or wrap the meat or cheese around a pretzel rod or breadstick.

* Involve your children in making the lunch, but be there to set some flexible limits. They can't have five cookies for dessert, but two or three are fine.

* Think fruits instead of fruit juices. They have more fiber and are more filling.

* Create your own Lunchables with little containers of canned fruit, applesauce, puddings or yogurt and put cheese and crackers in colorful plastic bags.