WASHINGTON (AP) -- The U.S. Food and Drug Administration says it will step up testing for a fungicide that has been found in low levels in orange juice.

FDA officials said they are not concerned about the safety of the juice but will increase testing to make sure the contamination is not a problem. In a letter to the juice industry Monday, the agency said that an unnamed juice company contacted FDA in late December and said it had detected low levels of the fungicide carbendazim in the company's own orange juice and also in its competitors' juice. Fungicides are used to control fungi or fungal spores in agriculture.

Carbendazim is not currently approved for use on citrus in the United States, but is used in Brazil, which exports orange juice to the United States. An FDA spokeswoman said the company's testing found levels up to 35 parts per billion of the fungicide, far below the European Union's maximum residue level of 200 parts per billion. The United States has not established a maximum residue level for carbendazim in oranges.

In the letter to the Juice Products Association, FDA official Nega Beru said the agency will begin testing shipments of orange juice at the border and will detain any that contain traces of the chemical. Because it is not approved for use in the United States, any amount found in food is illegal.

Beru said that because the FDA does not believe the levels of residue are harmful, the agency will not remove any juice currently on store shelves. But he asked the industry to ensure that suppliers in Brazil and elsewhere stop using the fungicide.

``If the agency identifies orange juice with carbendazim at levels that present a public health risk, it will alert the public and take the necessary action to ensure that the product is removed from the market,'' he said.

The discovery comes after the agency said it would also step up testing for arsenic in apple juice. FDA officials said last year that the agency is considering tightening restrictions for the levels of arsenic allowed in the juice after consumer groups pushed the agency to crack down on the contaminant.

Studies show that apple juice has generally low levels of arsenic, and the government says it is safe to drink. But consumer advocates say the FDA is allowing too much of the chemical _ which is sometimes natural, sometimes man made _ into apple juices favored by thirsty kids.

Patty Lovera of the consumer group Food and Water Watch said the federal government needs to rely on its own testing, not that of the companies.

``The federal government needs to set consistent, meaningful, enforceable standards for all toxins,'' she said.