Six billion by the year 2000?

Imagine the enormous crowd -- if every man, woman, and child living in Los Angeles could be gathered on one vast hillside. At the present rate of population growth, this vast assembly represents the number of people being added each month to the world's ranks -- swelling today's 4 billion to an astonishing 6 billion people by the turn of the century.

What would such a world be like?

Though no one knoes for sure, the experts expect a world far different from today's.

On the one hand, quantum leaps may have been made by then. The percentage of people enjoying benefits of modern technology and industry could have jumped from 12 percent in 1900 to 33 percent in AD 2000, according to an American Universities Field Staff report by Charles Gallagher.

However, today's radical diffeence betwen living standards in developing countries of the South and industrialized nations of the North are expected to grow much wider.

Over 90 percent of the population increase would be in the South, so that 4 out of every 5 people would be living in less-developed countries, says United Nations population chief Rafael Salas. India alone is growing by 1 million per month.

Already this poses a dilemma for leaders of these countries: How can life be improved for their people when each year adds to the number needing a share of scarce resources?

By AD 2000 a billion more jobs will be needed for children already alive today. And modern communications will probably intensify desires of developing peoples for services and amenities emjoyed in the North, says Dr. Paul Demeny of the Population Council in New York.

The search for jobs and the effects of what Mr. Salas calls the "aspiration explosion," would continue to encourage people to move from the countryside into the cites. The world's cities have doubled in population since 1950 and will double again by 2000, when, for the first time in history, more than half the world's population will be in cities, according to Mr. Gallagher.

In 1950 only six major cities had more than 5 million people. In the year 2000, there will be 60, 4k of them in developing countries -- with all the strains that will put on already overloaded sanitation and housing systems.

Enormous numbers of workers may be moving temporarily across international borders in search of jobs.

already this is happening in labor-short areas like Saudi Arabia, Kuwait, and Bahrain, where vast numbers of Palestinian Arabs and South Asians are living and working. The trend may develop in other countries that want to expand industrially but are short of manpower. West Germany is a prime example. The US must decide how many Latin Americans it will allow to settle within its borders -- legally or illegally. And all over the world, the rights of the migrant worker will become an important human-rights issue.

Finally, political effects could be dramatic. The 42 million population of Egypt, the country on which the US pins hopes for Middle East stability, is expected double in 20 years.

Muslims, who have one of the highest birthrates in the world, will account for one-fourth of the world's population by 2000, compared with about one-sixth at mid-century, says Mr. Gallagher.In Soviet Central Asia the ranks of politically restless Muslims will swell to one-fourth or one-third of the total Soviet population by the year 2000.

Not least, at the present rate, Arabs in Israel proper and Israeli-occupied lands will outnumber Jews by the turn of the century. Pressure could thus grow for Israelis to grant an independent state for Palestinian Arabs, says Nick Eberstadt of the Rockefeller Foundation.

Of course, questions remain.

Can the world actually sustain 6 billion and more people?

How long will it take for thinkers and technicians to find answers that will prevent overcrowding from producing pockets of discontent ripe for terrorist incitement? Or save forests from devastation in regions that depend on wood for heat? Or prevent economic disaster from overwhelming poor countries already stretched beyond their limits?

Will there be enough food in a world wher a country like China needs an amount equal to Canada's entire agricultural output just to allot a single handful of rice to each of its 1 billion people?

All these are challenges the planet must consider now -- while there is still time to make a difference.