A SECRET US plan to test MX missiles by firing them from California to the coast of Australia was signed off on by then prime minister Malcolm Fraser.

And it can be revealed that the federal Cabinet agreed to keep the intercontinental ballistic missile tests secret because it was "preferable for the matter not to become an election issue".

Details of the extraordinary plan, signed off by the most senior members of the Federal Government, are revealed in Cabinet papers released today by the National Archives.

Titled "United States Proposal Regarding Test Launch of MX Missiles", the file is marked "SECRET" and was presented to Cabinet by the defence minister James Killen.

The file notes that in June 1981 Cabinet had decided, after a verbal briefing from Mr Fraser, that there was "no objection in principle to the United States proposal".

Ronald Reagan, who was pursuing the strategic theory of Mutual Assured Destruction (MAD) against the Russians, was seeking a firm date and Cabinet discussed the plan again.

Mr Fraser had outlined the US proposal "for two test launchings of the new MX missile to the Tasman Sea off Cape Pillar".

The proposed words for an announcement to Parliament are included in the Cabinet submission.

It states: "I wish to inform the House that the Government has agreed to the US request and that two test launches will occur in January/February 1984. I would emphasise that the tests do not involve warheads as such and the missiles will not contain any nuclear material.

"The missile launch point is to be Vandenberg Air Force Base in California. The flight path does not pass over the Australian mainland or Tasmania. The nearest point to the Australian mainland will be some 220 kilometres east of Cape Pillar in Tasmania.

"In the very unlikely event that the missile moved off the pre-computed safety corridor of the flight path the missile would be destroyed.

"Assuming that we would not want a vessel fairly readily identified as a range instrumentation shop scheduled to call at an Australian port in the period October/November 1983, we could nominate July/August 1983 as the time for the ship visit and January/February 1984 as the time for the missile tests."

Thirty years on, in an interview with The Sunday Telegraph, Mr Fraser has revealed he would never agree to such missile tests today.

"If it was in today's world I wouldn't have agreed to it," Mr Fraser said. "The Cold War was still in progress. It was a different world.

"We've gotten far too close to the Americans."

The US wanted the first launch no later than the first half of 1984. A second launch was planned for 26 weeks after the first.

Cabinet was told a US Navy range instrumentation ship would need to survey the Tasman Sea impact area six months before the first test. Cabinet was told to keep details of the missile tests under wraps because "early announcement would allow time for activists to try to gather support and plan protests".

"The US will need to consider countries along the flight path of the missile and whether an early announcement in Australia and the US would create problems with, for example, Fiji or New Zealand.

"Consultation with the Tasmanian government would be necessary before a statement by the Commonwealth Government. It would be preferable for the matter not to become an election issue in either the Tasmanian state elections or federal elections."

The committee had agreed there was no objection in principle but there would need to be further consultations on "the details of the firings and, closer to the time, close attention to the details".

An announcement was proposed in the 1982 autumn sitting of Parliament.

"The Government of Tasmania will need to be informed before public announcement is made," the submission states. "There will be a requirement closer to the time of announcement for some additional material on, for example, the flight path to be available.

"Criticism will come from those concerned about the Reagan Administration's arms build-up and Australia's involvement with the development of United States strategic nuclear capabilities."

In 1985, the then PM Bob Hawke withdrew support for the missile tests after a meeting with US Secretary of State George Shultz.