DEFENCE Minister Joel Fitzgibbon has asked for an "urgent and full briefing" from his department about US plans to drop deadly nerve gas bombs on Diggers in Queensland in the 1960s.

The secret US plan to test the effectiveness of nerve gas agents, including sarin gas, in jungle warfare called for the Menzies government to lie to Australians about the nature of the tests to avoid a public backlash.

The revelations, which were contained in recently declassified top secret documents held by the National Archives, shocked Mr Fitzgibbon, who asked for an urgent briefing, promising no such tests would be considered today. The documents from 1963 to 1966 show the extreme lengths to which Washington sought to use its close alliance with Australia to further its own military research at the height of the Cold War, even at the possible cost of Australian lives.

Under the plan - which is not believed to have been acted upon - 200 Australian combat troops, presumably wearing 1960s-era chemical protection suits, were to be subjected to aerial bombardment in the Iron Range rainforest near Lockhart River in far north Queensland.

The nerve agents were to include VX and GB, better known as sarin nerve gas, both of which can cause almost instant death if they come into contact with skin.

The aim of the tests, illegal under international law, was to gauge the effectiveness of nerve agents in jungle warfare at a time when US military involvement in Vietnam was intensifying. The US proposal for nerve gas tests was made by US defence secretary Robert McNamara in July 1963, according to Defence Department and Prime Minister's Office documents obtained by the Nine Network's Sunday program.

The documents stated that of the 200 troops to be used in the tests, "only four to six would need to know the full details of the operation".

The US proposal recommended that the Australian government keep the nerve agent tests secret, describing them as either "equipment testing" trials or "land reclamation" experiments.

The Australian government is believed to have not responded to the initial US proposal in 1963, but in 1966 Washington approached the new prime minister, Harold Holt, with a request to drop tear gas on Australian troops. Again, Canberra quietly ignored the request.

Mr Fitzgibbon said yesterday it was "difficult to believe any such request came forward, but if it did, surely it would have been rejected by the conservative government of the day out of hand".

"I have asked Defence for an urgent and full briefing on this matter. I can certainly rule out any such testing in the future."

Former prime minister Malcolm Fraser, who was minister for the army from 1966 to 1968, denied knowledge of the US requests. He said it was "extraordinarily unlikely" the testing on Australian troops took place, although he could not rule it out.

"If anything like that had ever been put to me as army minister, defence minister or prime minister, I would not only have said no, I also would have queried ... with the American president: what the hell are your people doing?" Mr Fraser said.

He said he had no doubt Mr McNamara would regret the request. "I've gotten to know him quite well over the last 25 years, and I'm quite sure today he'd be thoroughly ashamed of that request," Mr Fraser said.

Peter Bailey, a former adviser to Mr Holt, told The Australian that the US request was taken seriously by the Australian government and he believed cabinet was divided on the issue.

He said Holt saw the implications of the request.

"He hadn't yet made his 'All the way with LBJ' speech - that was later in the year - but that was a reflection of his propensity to want to be with the Americans and do what they would like to do, but within reason, of course."

Mr Bailey said he briefed Holt on the implications, but Holt never discussed the request with him.

"There were really major issues about breaking international law, and a treaty that we'd signed up to and all sorts of defence implications," Mr Bailey said.

"And I'd seen what had happened to people who'd been gassed in World War I. They were still around at that time, lying out on verandas, ill, with very little comprehension."

Mr Bailey said the issue quietly went away - although he never saw any documents to suggest the government had rebuffed the request. He said he did not believe the testing took place, but it was possible it did. "It's one of those things governments quietly let drop at some point, and then it went away," he said.

Mr Bailey said the documents were first considered by the Defence Department, before coming to the attention of the prime minister.

Australia conducted extensive chemical weapons research during World War II as part of a joint program with Britain and the US.

About 1000 Australian soldiers were involved in mustard gas tests in Queensland in 1942.

British nuclear tests between 1955 and 1963 at the Maralinga site in South Australia resulted in serious health issues for many who were in the area.