TRENTON, N.J. — Can animal genes be jammed into plants? Would tomatoes with catfish genes taste fishy? Have you ever eaten a genetically modified food?

The answers are: yes, no and almost definitely. But according to a survey, most Americans couldn't answer correctly even though they've been eating genetically modified foods — unlabeled — for nearly a decade.

"It's just not on the radar screen," said William Hallman, associate director of the Food Biotechnology Program at the Rutgers Food Policy Institute, which conducted the survey.

Today, roughly 75 percent of U.S. processed foods — boxed cereals, other grain products, frozen dinners, cooking oils and more — contain some genetically modified, or GM, ingredients, said Stephanie Childs of the Grocery Manufacturers of America.

Despite dire warnings about "Frankenfoods," there have been no reports of illness from these products of biotechnology. Critics note there's no system for reporting allergies or other reactions to GM foods.

Nearly every product with a corn or soy ingredient, and some containing canola or cottonseed oil, has a GM element, according to the grocery manufacturers group.

In the Rutgers survey, less than half the people interviewed were aware GM foods are sold in supermarkets. At the same time, more than half wrongly believed supermarket chicken has been genetically modified.

So far, nonprocessed meat, poultry, fish and dairy products, and fruits and vegetables (both fresh and frozen) are not genetically modified.

GM food first hit supermarkets in 1994, with the highly touted Flavr Savr tomato, altered to give it a longer shelf life and better flavor. It flopped, in part due to disappointing taste, and disappeared in 1997, said Childs.

By 1995, farmers in several countries had planted millions of acres of GM corn and soybeans, and processed products containing them were in grocery stores.

Genetic modification of crops involves transferring genes from a plant or animal into a plant. Nearly all GM changes so far are to boost yields and deter insects and viruses, cutting the use of pesticides, thus making farming more productive and affordable — a particular aid to developing nations.

More than 80 percent of the soy and 40 percent of the corn raised in this country is a GM variety. Global plantings of biotech crops — mostly corn and soybeans and much of it for animal feed — grew to about 200 million acres last year, about two-thirds of it in the United States.

The one billionth acre will be planted this spring, according to the Biotechnology Industry Organization.