A quarter of adults in the city have elevated levels of mercury in their blood, linked to how much fish they eat, according to survey results released Monday by the health department.

Rates were higher among more affluent residents compared to those in lower income groups and were high among Asians, who eat more fish, the survey showed.

While mercury at the levels found in New Yorkers doesn't really pose a risk for most adults, the city suggested that children under 6 years old and pregnant and breast-feeding women avoid fish with high mercury contents over concerns that it increases the risk of cognitive problems in children.

"It's not bad for the average adult who isn't reproducing," said Daniel Kass, assistant commissioner for environmental surveillance and policy at the Department of Health and Mental Hygiene. "For a brief period of life, during pregnancy, while breast-feeding, it would be best to keep mercury levels down."

The health department released a brochure to inform people about the issue. It tells pregnant and breast-feeding women which types of fish have the lowest mercury counts and can be eaten more often and which should be eaten rarely or not at all.

Pregnant women could eat tilapia, herring or whiting up to five times per week because those fish are very low in mercury, based on an adult serving size of 6 ounces, the health department said. But they should not eat Chilean sea bass, swordfish or fresh tuna, which are too high in mercury, it said.

The mercury information came from the city's Health and Nutrition Examination Survey done in 2004. The survey, modeled on one done by the Centers for Disease Control and Prevention, is the first one of its kind done by a city, the health department said.

Among the survey's findings:

— New Yorkers in the highest income bracket averaged mercury levels of 3.6 micrograms per liter, compared to 2.4 micrograms per liter in the lowest income group.

— Asian women had mercury levels at 4.1 micrograms per liter; and among foreign-born Chinese women, 66 percent had mercury levels at or above 5 micrograms per liter, the point at which it must be reported to the state for monitoring.

— Among women in the 20-49 age bracket, the average level was 2.64 micrograms per liter, compared to a national average of 0.83 micrograms per liter among women in a similar age group.

Kass highlighted that fish has health benefits and that the city was in no way recommending that people stop eating it. He said the concern was making sure pregnant women had the best information.

"It's so easy to maintain a healthy fish diet without burdening your body with a lot of mercury," he said.

The health department brochure says to avoid fish caught in the East or Hudson rivers or in New York Harbor, which may have other contaminants.

The brochure, available through the city's 311 telephone information hot line, comes in English, Spanish and Chinese. Kass said that since the mercury levels were higher among Chinese women, the health department would be reaching out to groups that work with the Chinese community to make sure the word gets out.

The health department also is planning a study of fish eaten in Asian communities to test them for mercury levels.