Maryland had twice as many pollution-related beach closures and warnings last year as in 2000, reflecting a nationwide increase in closures at ocean and freshwater beaches, according to the 12th annual beach report released yesterday by the Natural Resources Defense Council.

"Testing the Waters 2002" found that Maryland had 262 beach closures and warnings last year, compared with 111 in 2000. The closings were mainly in Calvert, Cecil and Queen Anne's counties. Nationally, beach closures increased to 13,410 from 11,270, or 19 percent.

The report states that the rise in closures is partly because more municipalities are monitoring their beaches regularly.

High bacteria levels, indicating the presence of human or animal waste, accounted for 87 percent of beach closures nationwide last year, according to the report. Typically, contamination sources are sewage discharges and storm water runoff.

But in what the report called a "disturbing" finding, authorities could not identify the source of pollution in 54 percent of closures. In Maryland, 93 percent of 262 beach closings resulted from high bacteria levels, with 76 closures attributed to unknown pollution sources. Storm water runoff accounted for 42 percent of closings, 29 percent were due to sewage spills, and 16 percent to agricultural runoff, wildlife or boat discharges.