Consumer and environmental groups said the government had soft-pedaled the risk from eating large amounts of white tuna. "Tuna is a really popular fish and some people eat a whole lot of it," said Diana Zuckerman of the National Center for Policy Research for Women and Children.

While fish and shellfish are a good source of protein, nearly all seafood contains traces of methylmercury. High levels of mercury in the bloodstream of fetuses and young children can impair development of the nervous system.

In a joint advisory that updated guidelines issued separately, the Food and Drug Administration and the Environmental Protection Agency said shark, swordfish, king mackerel and tilefish should not be eaten by pregnant women, nursing mothers, children and women who may become pregnant. Methylmercury levels are highest in longer-lived, large fish.

The FDA and EPA said adults could eat up to 12 ounces per week of fish low in mercury. But they should eat no more than six ounces of white tuna or fish caught by family and friends.

The same guidelines on weekly consumption apply to children but they should be given smaller portions, officials said.

TUNA ALSO HIGH IN MERCURY

Fish sticks and fish sandwiches commonly are made using fish low in mercury, FDA said. Tuna steaks are higher in mercury and should be limited to six ounces a week.

On Thursday, the European Union's food safety authority recommended pregnant women limit consumption of fish, including swordfish and tuna, due to high mercury levels.

U.S. consumer activists said as a rule, light tuna had higher levels of mercury than shrimp, salmon, pollock and catfish, which were listed together as "five commonly eaten fish that are low in mercury."

An EPA researcher has estimated about 630,000 U.S. children are born annually with unsafe levels of mercury in the blood.

"What concerns me is how they buried this tuna information," said Zuckerman, by putting it toward the bottom of the one-page advisory.

White tuna contains three times as much mercury as light tuna, said Jane Halloran of Consumers Union. "It is essential FDA warn women of child-bearing age to limit their intake of albacore white tuna," she said.

The Environmental Working Group said the FDA "has actually made a bad situation worse, by encouraging consumption of albacore tuna at clearly unsafe levels." EWG said some white tuna can contain excessive amounts of mercury.