WASHINGTON (AP) -- Scientists have found a clue to the chemical reaction that may cause potato chips, french fries and other fried or baked starchy foods to build up high levels of a possible cancer-causing substance.

The suspect is asparagine, a naturally occurring amino acid that, when heated with certain sugars such as glucose, leads to the formation of the worrisome substance acrylamide.

The Food and Drug Administration has made studying acrylamide's risk and determining how to lower its levels in food one of its highest research priorities, according to a plan that agency officials were to discuss Monday with consumer groups and food manufacturers.

Canada's government made the discovery about the suspect chemical reaction and has ordered food manufacturers to look for ways to alter it and thus lower levels of acrylamide in food. Cincinnati-based manufacturer Procter & Gamble Co. says its scientists, too, have found the asparagine connection.

It is the first clue to emerge in the mystery of acrylamide since Swedish scientists made the surprise announcement in the spring that high levels of the possible carcinogen are in numerous everyday foods: french fries, potato chips, some types of breakfast cereals and breads - plenty of high-carbohydrate foods that are fried or baked at high temperatures. The chemical was not found in boiled foods, which are cooked at lower temperatures.

Sweden's findings were confirmed in June by governments in Norway, Britain and Switzerland, and preliminary testing of several hundred foods by the FDA suggests U.S. foods contain similar acrylamide levels, said Richard Canady, who is directing the agency's assessment of acrylamide's risk.

Acrylamide is used to produce plastics and dyes and to purify drinking water. Although traces have been found in water, no one expected high levels to be in basic foods.

It causes cancer in test animals, but it has not been proved to do so in people. Still, Swedish scientists have said the levels are high enough that foodborne acrylamide might be responsible for several hundred cases of cancer in that country each year.

In the United States, the FDA has been careful to caution that acrylamide so far is only a suspected carcinogen. The FDA has not yet advised consumers to alter their diets to avoid it.

Still uncertain is whether the FDA, once it finishes testing different foods next year, will publicly identify which brands contain the most acrylamide - information wanted by consumer advocates.

For now, Canady said, "We want to reinforce ... eating a balanced diet with plenty of fruits and vegetables. That's the best way to ensure that you're getting adequate nutrition."

The FDA has an impressive research plan but "should give the public better advice," said Michael Jacobsen of the consumer group Center for Science in the Public Interest.

"People should be consuming less french fries and potato chips for other reasons - the salt, the calories, the fat - and the government should have been urging that anyway. Here's yet another reason," he said.

The food industry stresses that while fried potato products are getting most of the bad publicity - most testing so far shows the highest levels in them - acrylamide is in a wide variety of foods. Procter & Gamble said Friday that its testing found acrylamide in such previously unimplicated foods as roasted asparagus and banana chips.

"The other aspect people need to look at is while a french fry or a potato chip may be high ... in concentration, it still comes down to what is the total contribution of that food to the diet," said Henry Chin of the National Food Processors Association.

Asparagine is in lots of vegetables, Chin noted.

Regardless, the asparagine clue is encouraging, Chin and Jacobsen said.

Different varieties of potatoes contain different levels of both asparagine and glucose. That might explain varying acrylamide levels among different brands - levels in french fries, for instance, vary widely among fast-food restaurants. Pick a different potato and a brand's acrylamide level might drop.

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