Each morning Phnom Penh awakens to find itself a little bigger than the day before.

Huddled together on sidewalks or in unused buildings are families newly arrived from the countryside, many of them refugees from villages that have run out of food. They come seeking work in government factories and offices, or in the city's bustling free markets.

The move to the city appears to be accelerating this year. Two months ago, Phnom Penh and its suburbs were officially reported to have 180,000 people. Today, the figure is 300,000.

Phnom Penh has long since shed its ghost-town atmosphere. From first light, its streets are alive with horse carts, bicycles and heavy trucks carrying soldiers and laborers.Entire streets are blocked off by hawkers selling vegetables and manufactured goods.

At night, electric lights and the glow of candles suggest that nearly every house and apartment in the city is occupied.

Parts of Phnom Penh today can pass for an ordinary Asian city. But this is counted as a mixed blessing by the 16-month-old Heng Samrin government and the foreign relief agencies assisting it. An overpopulated and unproductive city, it is felt, will drain resources from the countryside and inhibit the recovery of Cambodia as a whole.

The Vietnamese-backed government is grappling with the same problem the Khmer Rouge faced when they captured Phnom Penh in 1975: how to return people to the rice paddies, where Cambodia's most vital production takes place.

The Khmer Rouge settled on the drastic solution of evacuating the city at gunpoint. This eclipse of urban society is one of the most bitter memories Cambodians retain of the old government's rule.

Heng Samrin's restoration of the freedom to live in cities and engage in trade was tremendously popular, especially among the remains of Cambodia's middle class. Thousands of people now in Phnom Penh would probably have otherwise headed for refugee camps in Thailand.

The communist officials are reluctant to curtail this freedom, even though they feel it is out of hand, lest they evoke comparisions with their Khmer Rouge predecessors. To date, the government has limited itself to poorly enforced edicts that at best have slowed the city's growth slightly.

Moreover, many aid workers believe that the government, in its rush to secure a loyal civil service, has helped bring on the urban problem.

Civil servants in Phnom Penh get full rice rations, while the villages seem to get whatever is left -- usually only a pittance. The lure of full rations has drawn thousands to the city to seek work in government offices and factories.

But most jobs were filled long ago by people who made the move shortly after the Khmer Rouge were driven from the city in January 1979.

Other people come to the city attracted by the chance to trade. Sok Hieng, 20, a Chinese-Cambodian woman, moved to the city three months ago with nine family members from Prey Veng Province. She sells melons at a market just south of Phnom Penh.

Living on the second floor of a shophouse, the family has successfully carved out a niche in the city's vegetable trade, buying from farmers on the banks of the Mekong River and selling at a profit in the city. "We can do a lot of business here," Sok Hieng said. "In the provinces there aren't enough people to sell to."

Phnom Penh has spawned an endless collection of small businesses like theirs. People repair bicycles on the city's sidewalks. If they can find a scales and blowtorch to test purity, they buy and sell gold and silver. There are horsecarts for hire and barber shops.

Phnom Penh continues to grow despite government edicts cited as attempts to stop the influx. Provincial authorities, for example, are supposed to issue a travel pass before a prospective migrant can go.Migrants cannot reclaim their old houses if they find someone else living in it. They also cannot draw rations unless employed by the government.

A decree prohibits migrants from living in Phnom Penh's central district, on the theory that the less attractive housing in the outskirts will encourage them to go home instead.

In practice, these regulations seem loosely enforced. In some provinces travel passes seem to be issued almost routinely. Once in the city people move in with relatives alaready living in the restricted zones and share their rice rations.

Those unable to enter the city, meanwhile, have been willing to settle for makeshift dwellings on the city's outskirts. A huge shantytown with an active market stands along the road leading north from Phnom Penh.

In the provinces, the government has been more successful in controling the growth of towns. Large parts of Battambang town, for instance, seem as deserted as they were during the Khmer Rouge days.

"We don't allow ordinary people to live here," said a local official as he rode through the town's empty streets one recent evening. "Just soldiers and government employes." Private commerce is banned in the town's old market area, he said, but state enterprises will soon open for business there.

But on the outskirts of Battambang, too, thousands of merchants have set up thatch dwellings and are doing a roaring trade. Closing the old market does not seem to have dampened private enterprise in the province.

For the present, Cambodia is probably the most capitalist of the world's countries that call themselves socialist. But most analysts feel the current stage is only an interlude before private trading is curtailed and people are systematically sent back to the farms.

But in doing so, the Phnom Penh authorities will take the major risk of alienating the country's emerging middle class, and causing a new wave of refugees to the Thai border.