The occasion was so momentous that the news conference was held in the presidential mansion. The physicist and president stood before a throng of reporters and announced that nuclear fusion had been tamed.

The atomic energy that powers the sun had been mimicked in a secret power plant. Tets had successfully produced "the controlled liberation of atomic energy" without using uranium fuel, the president said. The discovery was "transcendental for the future life" of his nation, he said, and would bring it "a greatness which today we cannot begin to imagine."Such were the boasts of Juan Peron, the Argentine dictator, in March 1951.

But without a scientific paper to back up the claim, Peron's declaration met with skepticism among eminent American and European physicists. One of the doubters was Enrico Fermi, an inventor of the fission bomb. The technological leap from what was known about the physics of fusion to a working fusion power plant was too great to be believed.

Indeed, sometime later the Argentine press reported that the boastful physicist at Peron's side had been jailed for misleading him.

In the past month, scientists at the University of Utah have again raised the hope that man will be able to make useful, abundant electricity from the fusion of hydrogen atoms - drawing a virtually limitless fuel supply from the earth's seas. Their astonishing assertion - that in a simple electric cell they were able to create a continuous, net power-producing fusion reaction - is being met at once by suppressed excitement and great skepticism by the rest of the scientific community as it rushes to duplicate and verify their results.

Whether the new "fusion in a jar" method ultimately proves revolutionary or simply mistaken, the Utah scientists have already joined a grand tradition in the history of fusion power.

The utopian allure of a cure-all for man's energy needs has led many scientists over the years into sudden news conferences and premature declarations of victory. If the long-time fusion researchers are skeptical of the Utah scientists, perhaps they can be forgiven, for theirs is an unfortunate history marked by false starts and false claims amid incremental advances.

After Juan Peron came "Zeta." Those who have toiled for 30 years on the question of fusion power tell the tale of the British machine that once conquered fusion.

In 1958, on the eve of the declassification of this previously secret field, Sir John Cockcroft, the director of Harwell Weapons Laboratory in Britain, called a news conference that was attended by 400 reporters. He announced that a secret, experimental machine called "Zeta" - Zero Energy Thermonuclear Assembly - had produced constant temperatures in hydrogen gas of 5 million degrees centigrade. Neutron measurements indicated that thermonuclear reactions were taking place, Cockcroft said.

Zeta had apparently produced the world's first controlled fusion reaction - he was 90 percent sure, he said, under hard questioning.

The euphoria was dashed just a few months later. Further experiments showed that the crucial neutron count had been inflated by highly excited runaway particles that were not part of a true thermonuclear reaction. Overall, the hydrogen gas had not reached the ultra-high temperature thought necessary for fusion.

The Mighty Zeta proved to be a useful research tool over the next decade and also provided the overenthusiastic fusion scientists with an important lesson.

Since that time, news conferences in the field have tended to be modest, the announcements of progress always qualified by reminders of what still must be accomplished before man can make power from sea water.

The Utah announcement raises hope once again, but it also raises painful memories for scientists who have spent a lifetime pursuing an energy utopia that to date remains out of reach.