Lost civilization vanishing again?

IT all began with the discovery of a few red bricks upon a sandy surface. The year was 1922, and the British, intent on building a railroad, were scouting the Indus River Valley in the part of India that later became Pakistan. The bricks tickled the curiosity of an Indian employee, who started digging. Ancient ruins began surfacing.

That is how a civilization, lost in the night of time, came to be rediscovered. Further excavations revealed the existence of one of history's oldest empires, which flourished some 8,000 years ago. Efforts have been under way ever since to preserve this priceless testimonial to human history.

The discovery was all the more outstanding because, before it happened, the earliest civilization in the Asian subcontinent was thought to date from the 3rd century BC.

The town that excavations brought to light here dated from 2500-1500 BC, while further digging in the area uncovered human settlements dating at least to the 6th millennium BC.

The town, later named Mohenjo-Daro, overlooks the mighty Indus River as it follows its erratic course from the Tibetan mountains of Asia across Pakistan to the Arabian Sea.

Mohenjo-Daro occupies a unique position in our understanding of the first known human settlements and, perhaps more important, it represents the earliest known example of city planning. Built in a gridlike fashion with a large main street, it seems almost a minute version of Manhattan Island. It would be many centuries before the Romans constructed towns along similar patterns, and then millenniums before such rational municipal planning would be seen again.

The regular, ordered pattern of Mohenjo-Daro surprises the visitor. Each house was at least two stories high, built of bricks held together by mortar, and nearly every one had its own well. Water was supplied by a network of canals and drained through sumps in the streets. A large bath served as a meeting place and, probably, a place for religious functions as well. A 20-pillar hall might have been a courtroom.

The town's birth and its eventual abandonment are shrouded in mystery. What is known is that Mohenjo-Daro was the center of the empire of the Harappans, a Bronze Age people named after the city of Harappa in what is now northern Pakistan. They built a civilization in the Indus River Valley that rivaled Egypt and Mesopotamia and was more extensive than the two combined. It is believed to have reached from the Himalayan foothills all the way to the Arabian seaboard and eastward almost to Bombay.

The Harappans had their script, which is still undeciphered. They built oxcarts similar to those in use on nearby farms today, carved animals in terra cotta, and played a game similar to chess. Items of pottery identical to those produced in Mohenjo-Daro have been found in Mesopotamia and Iran, indicating the existence of an extensive trading network.

Despite extensive work on the site, some 75 percent of Mohenjo-Daro still lies buried. Excavation has been at a standstill for 20 years. Archaeologists cannot go further until the uncovered sites are consolidated and progress is made in halting their deterioration. Some of the structures unearthed by the British have already crumbled.

Remedial action began in the 1960s, and it has saved the town from completely disappearing. Realizing that dangerous deterioration was taking place, largely because of water damage from the nearby Indus, the Pakistani government appealed to the international community for help. The response provided a shining example of what international cooperation, channeled through UNESCO, can achieve.

UNESCO appealed internationally for funds and contributed technical know-how. Four UNESCO missions visited the area from 1964 to 1967. Archaeologists from Britain, Poland, France, and the United States were invited in 1968 to undertake a study of the danger facing the site. A further UNESCO mission of international experts visited Mohenjo-Daro in 1972 and, along with experts from Pakistan, prepared a master plan for it that minimizes the danger of further water damage.

Archaeologists from all over the world agreed that no effort was to be spared to save Mohenjo-Daro. Said Claude Schaeffer of France: ''No archaeological problem can be solved without reference to the Indus Valley civilization. For us , dealing with Mediterranean and Near East archaeology, Mohenjo-Daro is the easternmost horizon.'' And Prof.J. O. Brew of the US said: ''No archaeological site of such dimension can be found in any other part of the world.''

Methods for determining the relative ages of the structures were first introduced by George F. Dales, professor of archaeology at the University of California in Berkeley. These efforts are being continued by Dr. Michael Jansen with financial grants from the University of Aachen, in West Germany.

By using a specially constructed camera mounted on a ground-controlled balloon, Dr. Jansen has been able to make a complete stereo-photogram documentation of the whole area.

Worldwide financial contributions have enabled Pakistan to combat a variety of destructive elements besetting Mohenjo-Daro. The main scourge is water. With the proximity of the Indus River and a number of irrigation canals, and with the construction of a barrage to the north, the soil has become saturated.

By capillary action, water has been bringing the mineral salts found in the soil to the surface. As water evaporates under the warm climate, the salts react chemically with the baked clay, undermining the foundations and causing the walls to crumble.

The closeness of the site to the Indus constitutes another major threat, because the river often leaves its bed, changes course, and floods the area. Mohenjo-Daro is at its mercy.

The master plan provides for lowering the ground-water level from the present 6 feet to 60 feet by means of a pumping system, diverting the course of the Indus, and restoring and preserving the buildings by removing the mineral salts. The plan also includes electrification of the site to power equipment and to move more closely to exploiting the site's tourist potential.

Of the $16 million needed to carry out the master plan, $9 million still must be raised.

''Mohenjo-Daro must be preserved so that the progress of humanity can be studied effectively,'' declares Muhammad Ishtiag Khan, Pakistan's director general of archaeology.

Further excavations in the years to come may unveil the mystery of Mohenjo-Daro's abandonment. Several theories have been advanced, none of them conclusive. It has been suggested that the inhabitants were slaughtered by the invading Aryans. Is that why Mohenjo-Daro means ''Mound of the Dead''?