A poisonous substance in the same class as arsenic has been found improperly packaged at the General Services Administration's Curtis Bay strategic materials stockpile near Baltimore. It was the second instance this year of a potentially dangerous situation at that stockpile depot.

The substance -- mercuric oxide -- was to be sold in September, but a bidder informed GSA officials that the compound was packaged in wooden kegs that did not meet Department of Transportation shipping regulations. Those regulations require cases for "B-class poisons," such as arsenic compounds and mercuric oxide, to withstand a two-foot drop on concrete and GSA officials said they were uncertain that the 35-year-old crates would hold up.

GSA withdrew the bid offer in October based on the contractor's warning.

The mercuric oxide was last handled by federal workers in the 1940s when it was transferred from the U.S. Navy to the stockpile. It was used to paint the hulls of ships during World War II to prevent corrosion.

In May, Nathan L. Adler, director of GSA's Inspector General field office in New York, reported that there were leaking drums of radioactive thorium nitrate at Curtis Bay. The report said the problem was first studied in 1979, but "at the time of our visit in 1982 , these conditions remained unchanged."

"We observed patches of rust, as well as bullet holes, in some of the drums," Adler wrote.

J. Wayne Kulig, associate director of the GSA stockpile, said Wednesday he strongly disagreed with the audit but acknowledged that the thorium nitrate has not been repackaged. Kulig said a new fire control system is being installed in the building where the thorium nitrate is housed and handling the material without the sprinkler system is dangerous.

The inspector general's audit also found problems in depots at Mechanicsburg, Pa., and Point Pleasant, W. Va.