The Czechoslovaks call them rakosi--the reed people. They are young Vietnamese migrant workers, arriving in Czechoslovakia with four- to six-year contracts to work and learn skills in Czechoslovak factories and manual trades.

In 1979, they came from northern Vietnam, clothed in austere gray suits that caused the Czechoslovaks to liken them to the Chinese. But since 1982, a new wave has filtered into the country. These are the southern Vietnamese. They differ radically from their colleagues to the north and their presence in Czechoslovakia has caused problems.

Long-haired, sneakered, with playboy sunglasses and Adidas jackets, they spurn the ways of the northern Vietnamese and show an unconcealed fascination with America.

One young Vietnamese told western travelers: "America--a little war, but good. Russia--a little peace, but bad."

Last month western diplomats in Hanoi reported that people were paying bribes to get sent to the Eastern European countries after having seen the consumer goods that the lucky ones were sending back home. From the Czechoslovak vantage point, however, the rush had already begun in April 1982, when 14,000 Vietnamese were officially reported as being in the country. Now the official number is 30,000, and a recent Prague broadcast indicated the figure would continue to climb for at least another year before beginning to taper off.

Despite the language courses made available by the Czechoslovak authorities to the arriving Vietnamese to help them overcome the cultural barrier, it seems increasingly evident that neither the Czechoslovaks nor the Vietnamese have been adequately prepared to deal with the situation.

In December 1980, Hanoi signed a labor cooperation treaty with Prague that had two goals: first, it would relieve Czechoslovakia of a growing labor shortage while providing skills for thousands of Vietnamese workers. They, in turn, would go home to reinvigorate Hanoi's own moribund postwar industries.

It was also to be a way for Vietnam to repay some of the huge debts that the Soviet Bloc had extended to it in material aid and long term credits. The laborers, in effect, would pay two-thirds of their salaries back to the Czechoslovak government and be reimbursed at home in Vietnamese currency.

The pay arrangement and false expectations of what awaited them in Eastern Europe appear to have led to frictions.

Late last summer a Vietnamese working in a shoe factory allegedly murdered a doctor for refusing to give him sick leave.

The official Czechoslovak press, which had ignored the problem, finally published an article in August. Mlada Fronta, the official Communist youth newspaper, said, "Until not so long ago, our enterprises had the best experiences with Vietnamese trainees, but some workers who have arrived recently have so far in some places failed to meet expectations."

According to Czechoslovak sources, a hundred Vietnamese working in a technical-parts factory went on strike in early winter to demand higher wages. Having arrived with specialized skills, they had been placed in unskilled jobs and been given correspondingly low wages.

The strike lasted a little over a week, sources said. When it was over, two or three of the leaders were forcibly sent back to Vietnam at their own expense--a sum that could take several years for a Vietnamese to repay.