LONDON (AP) _ A former Australian prime minister sent a coded message of outrage and shock to his British counterpart in 1956 after a radioactive cloud from a British nuclear test drifted over the Australian mainland, an investigative tribunal was told Friday.

Bernard John Perkins, 49, a former radio operator with Britain's Royal Navy, said Sir Robert Menzies sent the message to British Prime Minister Sir Anthony Eden following the second of two test blasts that year on the Monte Bello Islands, located 60 miles off western Australia.

The coded message said: ''What ... is going on? The cloud is drifting over the mainland,'' Perkins told an Australian Royal Commission that is in London to investigate the nuclear tests Britain carried out in Australia between 1952 and 1963.

The message from Sydney ''was written down on a pad in manuscript by the operator who took it,'' said Perkins, who was aboard a Royal Navy ship near the test. ''The pad was on the table, and we were all reading it.''

Perkins, who visited the test site seven days after the first blast, said he was discharged from the Navy in 1960 as an epileptic and has since been treated at psychiatric hospitals for personality disorders.

He said he received one shilling (then 14 cents) a day in hazardous duty pay during the tests.

Retired British Army Col. Peter Anthony Lowe, 65, testified that he was an observer during atomic tests at Maralinga in the southern Australia desert in 1956.

Lowe, who was 5 miles from the detonation site, said his stomach was removed in 1973 after he contracted cancer.

''The most vivid recollection I have was the effect of the heat on the back of my neck,'' he said.

Lowe said he observed a second blast from inside a tank, which was moved 10 feet sideways by the blast.

Denis Edward Tilling, 48, a Royal Air Force serviceman who drove into the Maralinga test area in 1957, said he developed abscesses on his arms, wrists and hips afterward during his voyage home to Britain.

''There was no explanation at all by the authorities about the effects of radiation,'' Tilling said. He told how the servicemen ''were showing off their red necks caused by their nearness to the explosion.''