Those teeming thousands demonstrating in the shadow of the Kremlin must look threatening to Mikhail Gorbachev, as he thumbs dejectedly through yet another report on the Soviet Union's economic decline. They look increasingly sinister to westerners too. Even before two boatloads of fleeing Albanians arrived on Italy's reluctant shores, it was clear that the crumbling of Europe's communist bloc would drive many of its citizens to seek their fortunes in the West. Once western governments began worrying about immigration from east to west, they noticed that even larger numbers would want to move from south to north. Immigration, with all its uncomfortable baggage of racism and nationalism, is set to become one of the hardest issues for liberals to handle, because the old liberal preference for an open-door welcome is not going to work any more.

Already, developed countries are receiving immigrants from new places, and on an unprecedented scale. America accepted more immigrants in the 1980s than in any previous decade in history. And immigrants of a quite different kind in 1965 the proportion of European to non-European immigrants was nine to one; 20 years later that ratio had been reversed. The long-term consequences of the change will be huge. Today more than three-quarters of all Americans are white; by the middle of the next century that proportion may have fallen below half. Among California's schoolchildren, it already has. As one American pundit puts it, People of 30 and older will increasingly have the experience of growing up in one kind of country and of growing old in another. In some parts of the United States, Americans will thus share the experience of new immigrants simply by staying at home.

The way rich countries react will depend partly on their past. America, a land built by immigrants, has a strong commitment to welcoming newcomers. Europe, by contrast, has traditionally exported people. Its southern countries - Spain, Italy, Portugal, Greece - remained net exporters well into the 1970s. Even when northern Europe began to recruit workers in Turkey, Yugoslavia and the Caribbean, the myth persisted that these were temporary guests, who might one day go back to where they came from. Yet several European countries are now home to more foreigners, proportionately, than the United States. Over 8 percent of Britain's population and 11 percent of France's are foreign-born, compared with 6 percent of America's.

More will come. The first rush, from Eastern Europe and the Soviet Union, has already begun, with roughly 2 million people leaving there last year. As unemployment sweeps through Eastern Europe and the Soviet Union disintegrates, the numbers may continue in the low millions in each year of the 1990s. The citizens of Western Europe, already suffering from rising unemployment, are deploying troops to keep out refugees at the old Iron Curtain.

Immigration...is set to become one of the

hardest issues for liberals to handle,

because the old liberal preference

for an open-door welcome

is not going to work any more.

Immigrants from Eastern Europe and the Soviet Union will be easy to absorb, though, compared to what may follow. The communist countries, present and former, are lands of stable or falling populations. Given two decades of economic recovery and (harder to predict) an absence of ethnic strife, Western Europe's eastern neighbors will mostly prefer to stay at home. Even most of those who move will share with their hosts a common inheritance in terms of race, religion, education and culture. They are, after all, Europeans.

Not so most of the potential immigrants from the south. The population of the world's poorer countries is growing twice as fast as Europe's did at its peak in the late 19th century, when its huddled masses crossed the Atlantic. The population of the rich world will probably stabilize well below 2 billion, but in poorer countries the numbers will rise from about 4 billion now to more than 8 billion and maybe, in 40 years or so, to more than 12 billion. Most of those billions may prefer to stay home, but the movement of even a tiny fraction would appear to northerners as an invasion.

Plenty of pressures will encourage people to leave the third world. Lack of jobs, lack of land and lack of water will squeeze living standards at home; education and television will paint rosy visions of better lives abroad. Cheap air fares will make the journey worth the gamble. Northern employers, anxious for adaptable young brawn as native workers age and become set in their ways, will be willing allies.

A DOZEN MILES ACROSS THE MED

The greatest gap, demographic and economic, will yawn between the two shores of the Mediter-ranean Sea. Earnest Spanish civil servants already talk of Europe's 'southern flank'; the military overtones, the sense of siege, are unmistakable. For while the growth of population has started to slow down in Latin America and Asia, the lands from which most of America's latest immigrants have come, in much of Africa it is still accelerating. And though real incomes in North America are far higher than in Latin America, the gap between Africa and Europe is almost twice as great.

As Africa grows younger, Europe ages. On the Mediterranean's southern shore, the average woman has between four and six children; on the northern shore, between one and two. Each year one million more babies are born in the countries of north Africa than in the European Community. By 2025 a number of African countries that now seem medium-sized will have populations that equal or dwarf those of the larger countries of Europe. Turkey will have 20 million more people than united Germany; Sudan as many as France; Egypt as many as Spain and Italy combined. The fastest growth will be among the young, the age group most willing to do a Dick Whittington. To a youngster in Cairo's slums, Italy will seem a land of fabulous wealth. Measured in terms of purchasing power, its living standard is four times that of Egypt. And Egypt is rich by sub-Saharan standards.

For white liberals...the hardest thing

is to recognize that the scale

of immigration changes the way

countries react to immigrants.

TAKE THE WEALTH TO THE PEOPLE

For white liberals, brought up to believe in equal human rights and free movement of labor, the hardest thing is to recognize that the scale of migration changes the way countries react to immigrants. Today, no country in the world allows free immigration the voters would not stand for it. As the number of aspiring immigrants grows, only tough controls will insure the safety of those black and brown workers who have already arrived. Other-wise, all will risk persecution as gate-crashers. To minimize racism at home, many countries need to have racist controls on immigration.

But even the toughest controls will not stop people from trying to climb over the gates if conditions back home are desperate. Rich countries will bully and bribe poorer ones to hang on to their citizens. Aid programs will emphasize jobs, not just investment. But trade will help more than aid. If poor countries are to boost the incomes of their spiraling numbers, they need to create jobs. Yet the most labor-intensive industries - textiles, metal manufacturing, engineering, food processing - are all ones where rich countries struggle most fiercely to protect their own markets. Absurdly, those industries often survive in richer lands partly by employing cheap immigrant labor. Wise governments will let jobs go to the countries that can do them most efficiently.

As for companies in today's industrialized world, they should stop clamoring to import workers and take their investment abroad instead. Japan has chosen to export capital rather than import labor; western companies must copy it. If, as a result, poor countries grow rich faster than the already-wealthy, all to the good. If foreign trade and investment do not narrow the gap between rich world and poor, then vast movements of humanity will try to do so instead.