Court documents filed Tuesday by Dow Chemical Co., a defendant in a suit initiated by Vietnam veterans, show that the Army may have known of the potential danger of dioxin in Agent Orange at least two years before the defoliant was sprayed in Vietnam.

Dow Chemical filed the documents in U.S. District Court, where a suit has been brought by Vietnam veterans against Dow and four other chemical firms that manufacture the pesticide. The veterans say their exposure to dioxin, a highly toxic contaminant, caused a variety of ills ranging from tumors to birth defects and nervous disorders.

Dow produced a scientific paper published in 1962 in the Journal of Investigative Dermatology that details a technique for testing dioxin's potential for harm by using the tissues of a live rabbit's ear. The study, a footnote indicates, was financed by the Research and Development Division, Office of the Surgeon General, Department of the Army.

The paper refers to another investigation of dioxin's toxicity to humans first reported in 1957 in a German scientific journal, which also is included in court papers.

The chemical companies produced the defoliant under Department of Defense contracts during the Vietnam war. About 2,000 Vietnam veterans from 24 states have joined in the suit, which has yet to come to trial because of procedural delays.

Both the veterans and the chemical companies have contended that the Department of Defense may have been aware of the toxic potential of dioxin in 2,4,5-T, one of Agent Orange's two herbicidal components. But until now, neither side had offered evidence to substantiate that contention.

"So far there have been mainly allegations," said Don Frayer, an officer of Dow's legal claims division. "This is a fact, the first offered so far."

In its legal papers, Dow said Tuesday that the federal government knew as early as 1962 that dioxin was produced during the manufacture of 2,4,5-T; that dioxin was toxic, could be detected and, in animals, could cause liver damage as well as chloracne, an eruption of the skin, loss of appetite and debility.

Joan Bernott, an assistant U.S. attorney handling the Agent Orange case for the government, said she could not comment on the allegations and the documents until she received copies.

"It's moving things off dead-center," said Victor Yannacone, chief counsel for the veterans. "It moves the litigation for the first time away from procedural maneuvering and toward substantive issues supported by documentary evidence."