The great Minoan civilization -- sometimes called the first great socialist state, and identified as Plato's lost Atlantis -- declined abruptly after a volcanic eruption apparently caused the evacuation of one of its chief islands some 3,500 years ago.

Much archeological work has attempted to date the great eruption, which would enable scientists to place an end bracket on the Minoan period in the Mediterranean. So far they have been unable to place the date more accurately than within a 200-year period. A date of about 1500 B.C. has long been accepted.

But now volcanologist C.U. Hammer of the University of Copenhagen and his colleagues in Denmark have applied a different technique to the problem and say the accepted date may be off by about 150 years.

Hammer took an ice core in Greenland and measured the acidity of the annual deposits over a period from 1900 to 1300 B.C. In about 1645 B.C., plus or minus 20 years, he found a sharp rise in acidity for the whole year and a deposit of sulfuric acid, which would be consistent with a major eruption that spewed ash into the world weather system.

The eruption took place on the island of Thera, now called Santorini, where the ancient metropolis Akrotiri was situated. Akrotiri has been called the prehistoric Pompeii because of the rich remains found under volcanic ash. Thera is located about 75 miles north of Crete. Minoan culture was centered in Crete, with its capital at Heraklion.

If the new date can be verified, archeologists will have to begin a scramble to revise the dating system of the whole Minoan period, expanding the "Late Minoan" era to before 1700 B.C. and cutting short the "Middle Minoan" period of massive building projects by more than a century.