Not long ago, citizens of Shenzhen, the Chinese fishing village that nearly overnight became a model trading city, boasted that their slogan was "Work hard, play hard." But local officials say Shenzhen must now drop the "play hard" part of the motto and do more work.

"Playing hard is not suitable to the needs of an economically backward country," said one official here.

So many problems have come to light here, including foreign exchange speculation, unproductive trade practices and even some cases of prostitution, that Shenzhen no longer looks like the model it was intended to be.

Shenzhen was the first, most important and fastest growing of the four special economic zones established by the Chinese government in the early 1980s to attract foreign investment and technology. Shenzhen has more high-rise buildings, as well as amusement parks, than a number of Chinese cities many times its size.

Many of Shenzhen's more than 300,000 citizens are feisty young go-getters who came here to advance their careers and standards of living. Many have been rewarded by earning wages in some cases double those of their parents or double those provided for equivalent work elsewhere in China. Many earn more than central government ministers. And they are proud of what has been accomplished here.

"Shenzhen's young people are willing to take risks," said a Chinese journalist stationed in Shenzhen. "There's a Chinese saying that the bird that sticks its head up is the first to get shot, . . . but Shenzhen people are willing to stick their heads up. They are willing to attract attention."

Among those working here are said to be the sons and daughters of a number of Chinese leaders, including those of Premier Zhao Ziyang and Communist Party General Secretary Hu Yaobang. The daughter of Ye Jianying, a retired member of the ruling Politburo standing committee, heads a film studio in Shenzhen.

Shenzhen is one of China's biggest windows on the outside world, a place where Chinese can learn about high technology and western methods of trade and finance.

Shenzhen also was designed to give the people of nearby Hong Kong a sense of confidence in the future of China, which is supposed to resume sovereignty over Hong Kong in 1997.

Chinese officials also apparently hope that if Shenzhen and the other three special economic zones succeed in showing that the Chinese Communists can deal with a mixed economy, allowing some private initiative, it might make it easier for Taiwan to consider reuniting with the mainland.

But rather than attracting high technology and multinational corporations, Shenzhen has drawn in low technology and small investors.

Many Hong Kong manufacturers are taking advantage of Shenzhen's open spaces and its wages, which are lower than those paid in Hong Kong. Total foreign investment in Shenzhen comes to about $800 million. But China has spent more than $1 billion constructing facilities designed to attract foreign investors.

While the zone was meant to earn foreign exchange through exports, most of its trade has been with the interior of China. Much of that trade has consisted of illicit deals for imported consumer goods that have reduced the country's foreign exchange while adding nothing to its wealth, according to reports in the official Chinese press.

In June, China's top leader, Deng Xiaoping, reacted to Shenzhen's problems by stating that the pioneering economic zone was only an "experiment," making its future sound less than certain.

"We have yet to see whether this course is right or not," said Deng, in sharp contrast to the upbeat remarks he made about Shenzhen a year earlier. "We hope it will succeed. But if it fails, we can draw lessons from it."

Deng's comment startled some foreign investors, and, to reassure them, Chinese officials quickly began making statements in support of the special economic zone. At the same time, however, the central government replaced Shenzhen's mayor and began to reassert more control over the zone's finances.

Shenzhen city legal authorities disclosed early last month that they had uncovered illegal transactions in foreign exchange amounting to more than $100 million.

Much of what one sees in Shenzhen does not appear to have been thought through carefully. A plan to create a special currency for Shenzhen apparently has been dropped. The city appears to be building too many hotels and office buildings. High-rise buildings are not necessarily the safest or most efficient structures, but Shenzhen has insisted on having them.

"There is no real need for high rises in Shenzhen, because land is easy to get," said an urban planner in Hong Kong. "High rises are difficult to build, and Chinese firefighting techniques are not up to handling fires in 30-story buildings. But to the Chinese, high-rise buildings mean modernization."

Viewed in a broader perspective, however, many of Shenzhen's problems would appear to be understandable at this early stage in its development.

Lawrence C. Reardon, a Columbia University graduate student doing research on the economic zones, said there has been a lot of "sensationalism" in the western press reporting on the zones.

"Experience elsewhere, in Taiwan, India and South Korea, has shown that all these countries had problems in developing such zones," he said.