The neatly dressed young man on the plane from Peshawar was reading a paperback titled, "How to Increase Your Sales."

It was one of those typical Dale Carnegie type tracts of Western capitalism, with chapter headings like "Sell Yourself Before Your Product." It would help him in his work selling drugs for an American chemical company.

He was, he said, a Marxist.

He'd grown up in a small village, the third of seven children. "Our people are very backward and poor," he said impassionately. "They live in very bad conditions and barely have enough to eat. The rich capitalists of the world exploit them every day."

The young man had a knack for selling, and he worked hard at it. At a time when hundreds of Pakistani university graduates were without work, his job paid very well.

But the Dale Carnegie Marxist was convinced that a brighter future awaited him somewhere far from the squalor of Pakistan's overcrowded cities. Like thousands of other young, ambitious Pakistanis, he was making plans to leave the country.

The movement represents a serious drain on the country's most valuable resource - its smartest, best-educated young people. The phenomenon called the "brain drain" is repeated each day in dozens of Third. World countries as thousands of the best and brightest leave home seeking a better life in the Middle East, Europe or the United States.

Tragically, the people who leave are often precisely those the countries need most: doctors, lawyers, teachers, highly trained engineers, planners and skilled technicians.

A quarter of all the doctors in Britain, for instance, are immigrants. The majority have come from India and Pakistan, country's with staggering health Problems.

An estimated 40 per cent of all the physicians trained in the Philippines ultimately wind up in the United States.

Some nations have placed tough restrictions on emigration. Others are making major efforts to lure professionals back to their home countries.

But the brain drain continues, and the forces drawing young men and women away from Karachi and leading them to New York or London are not particularly hard to understand.

The young Marxist was planning to join a brother and sister who had already moved to England.

"They say things aren't so hot for Asians in London," he said. "But life has got to be better there than it is here."