Mega-muffins have become the norm. A pretzel from a street vendor is as much food as five slices of bread, a simple cup of coffee has turned into a pint, and beers are starting to come in 22-ounce sizes. Chocolate truffles? Some are as big as hens' eggs.

This has long been a land of size: big spaces, big cars and big buildings. Now there are signs that food is getting bigger than ever. Restaurants are heaping huge quantities on plates to attract customers who demand more for their money.And consumers gobble rice cakes by the bag as they heed the siren call of fat-free labels while forgetting that fat-free can still be fattening.

Two trends of the '90s - getting value for money and eating low-fat or fat-free foods - have become invitations to gluttony.

And so, despite all the publicity given to the federal government's food pyramid and all the nutrition information on labels, Americans are getting bigger. The latest statistics from the Centers for Disease Control in Atlanta show that one-third of the population is overweight, up from a steady 25 percent from 1960 to 1980.

"We overeat because too much is served," said Sachiko St. Jeor, the director of the nutrition education and research program at the University of Nevada School of Medicine in Reno. "When it's there, we eat it."

Nutritionists are beginning to look at the amount of food people eat, not merely the amount of fat. They are dusting off the notion that calories, not just fat percentages, make a difference.

Diane Morris, the president of Mainstream Nutrition, diet counselors in Winnipeg, Manitoba, said she has had clients who have gained 10 to 15 pounds eating low-fat and fat-free foods.

Nutritionists agree that a clearer message must be communicated.

"People have the idea that if you're eating less than 30 percent fat you can eat all you want," said Eileen Kennedy, a nutrition policy coordinator for the office of food and consumer services at the Department of Agriculture. "We haven't been clear enough on serving size."

One source of confusion is the huge gap between the serving sizes listed on food packages and the servings people actually eat at home and in restaurants.

Labels on boxes of pasta, for instance, define a serving as two ounces uncooked. Usually, that means 200 calories. But most cookbooks recommend a four-ounce serving - and restaurants typically boil seven or eight ounces for each portion of pasta. That's perhaps 800 calories - without the sauce.

Do consumers bother to do that arithmetic? While foods like pasta may be perfectly healthy and even free of fat, people still gain weight if they consume them in large quantities.

Dr. F. Edward Scarbrough, the director of the Office of Food Labeling for the Food and Drug Administration, maintains that the two-ounce portion of pasta, like the other serving sizes on the new standardized labels, was derived from studies that tried to determine the amounts people customarily consume at a meal. "There is not much reliable data on the subject, especially since it's based mostly on recall," he said.

He cautioned that the serving sizes were never meant as recommendations. "Our objective was to provide a method for comparing products on store shelves," he said.

Bonnie Liebman, the director of nutrition at the Center for Science in the Public Interest in Washington, said: "Most people think the serving sizes on food labels are gross underestimates. People eat much, much more."

Perhaps because they are paying for it.

"Our average portion of fish is 13 ounces, and people finish it," said Alan Stillman, whose company, New York Restaurant Group, owns restaurants like Smith & Wollensky, the Manhattan Ocean Club and the Park Avenue Cafe that are known for large portions. The portions are big, he said, because customers demand them. "Restaurants serving minute portions have gone out of business."

Indeed, the idea of providing lots of hearty food for the money, like the mountain of pasta or the foot-long hot-dog, reflects a swing away from the artful little rosette of food in a sheer pool of sauce that typified nouvelle cuisine of the 1980s.

The only legacy of nouvelle cuisine is the oversize dinner plate. But now it comes piled to the edge with food. In some restaurants, it takes a salvage vessel to recover a fork that accidentally slips into the bowl of fish stew.