A former supervisor at Kerr-McGee Corp.'s plutonium plant testified today that he and co-workers never found 40 pounds of plutonium that turned up missing at a plant where Karen Silkwood worked.

In testimony during the third day of the $11.5 million Silkwood contamination trial in U.S. District Court, James V. Smith, 47, of Guthrie, Okla., said the search was stopped by company officials as a plant closing deadline neared.

An atomic scientist testified last week that four pounds of the highly radioactive element is enough to make a nuclear bomb.

Kerr-McGee lawyers had unsuccessfully sought to block Smith's testimony and the company's chief counsel, Bill Paul, was overruled on nearly 20 objections during Smith's testimony.

Silkwood died in a 1974 auto accident. Her survivors filed the vivil lawsuit alleging she and her apartment were contaminated by plutonium through company negligence.

The company claims Silkwood contaminated herself, possibly to dramatize her claims about poor safety practices.

Smith was the supervisor of the first step in the nuclear fuel manufacturing process when Kerr-McGee's plutonium plant near Crescent, Okla., closed in 1975.

Before the plant closed, Smith said he and his crews spent "many thousands of hours" flushing pipes where liquid plutonium was handled in an attempt to account for the missing amount.

Kerr-McGee has acknowledged the plutonium is missing, but lawyers for the firm contend it is still in the pipes at the plant.

Asked if there was any security to prevent plutonium from getting out of the plant during the term of the first contract, Smith said, "There was none of any kind -- no guards, no fences, no nothing."

He said there was increased security after 1972, but it didn't really tighten up until Silkwood's death.

Smith said that conditions in the uranium plant -- on the same site as the plutonium plant where he worked -- at times were so bad it was nearly impossible to breathe because of ammonia and uranium fumes.