Maryland environmental officials warned yesterday that eating fish from the northern branch of the Potomac River could increase the risk of cancer.

The health advisory from the Maryland Department of the Environment said fish caught on the river between Luke and Paw Paw, W.Va., might be contaminated with dioxin, a suspected cancer-causing chemical. The chemical is a byproduct of a bleaching process at Westvaco Corp.'s paper mill in Luke.

West Virginia advised residents last summer to limit consumption of fish caught fewer than 70 miles downstream from the Luke mill.

Maryland environmental officials released the advisory for the 70-mile section of the river in Western Maryland after the federal Environmental Protection Agency urged them to issue a stricter dioxin warning for fishermen and area residents.

Although the Westvaco mill has reduced its dioxin discharges in the last year, EPA scientists said the chemical has accumulated in river bottom mud, where it can contaminate fish for years.

Westvaco has implemented changes in its manufacturing process that have reduced dioxin in its wastewater by more than 90 percent. The concentration of dioxin discharged to the river has not been detectable in nearly all samples collected since 1989, company officials said.