Some microwave packaging may disintegrate when exposed to high cooking temperatures, causing potentially harmful chemicals to enter food, a federal report stated.

Those containers most likely to pose problems are known as heat susceptors designed to elevate temperatures--some to 500 degrees F.--during microwaving.

The packaging is used on such traditional microwave products as popcorn, pizza, French fries, fish sticks and Belgian waffles, according to the U.S. Food and Drug Administration.

Typically, the susceptors are marketed as "browning" or "crisping" devices. The microwave would be unable to brown food--as is the case in conventional ovens--without the presence of these items in the packaging.

The agency's concern also extends to plastic "dual ovenables," or those containers prepared for use in either the conventional or microwave oven.

"The FDA is concerned . . . . that such high-temperature use of these materials may cause packaging components such as adhesives, polymers, paper and paperboard--known as indirect food additives--to migrate into food at excessive levels," said a recent report in FDA Consumer magazine.

The agency identified at least two compounds that have migrated from microwave packaging directly into food. In a September, 1989, test of microwave French fried potatoes, federal researchers found minute levels of polyethylene terephthalate in addition to diethylene glycol dibenzoate.

Since 1987, the agency has requested that the packaging and food industries voluntarily provide research indicating that partial dissolution of these materials, and subsequent migration of the chemicals into food, is safe. The information has not been forthcoming.

As a result, FDA has stepped up its efforts and published a notice last year that establishes a deadline for manufacturers to submit the data.

The FDA must approve all additives--direct or indirect--that may be consumed in processed food. Even unintended results, such as the leaching of chemicals from microwave packaging, must receive the agency's approval.

Yet, in its report on the problem, the FDA made an unusual concession. It stated that the agency had not been "ready" for the introduction of these packaging innovations and was surprised to learn that the devices could raise microwave oven temperatures to 500 degrees.