Bangkok — Exactly 200 years ago, a newly chosen King of Siam, Chao Phya Chakri, moved the capital of his kingdom to a marshy lowland where he thought his people could grow rice.
The birth of Bangkok, thus, coincided with the start of Thailand's longest-lasting monarchy. While the Chakri dynasty remains revered, the city long ago lost its agricultural purpose and today ranks with government bureaucracy as a major economic problem.
''How we solve Bangkok's urban ills will determine our future,'' says Dr. Snoh Unakul, secretary-general of the National Economic and Social Development Board.
Only 16 percent of Thailand is urbanized. But 60 percent of the urban population lives in Bangkok, which is 45 times as big as the next largest city, Chiang Mai.
Loss of productivity can be measured by the two-hour commutes -- mostly idling in traffic -- for many workers. Such a concentration of urban wealth creates large income disparities with the rural poor, and government officials find it difficult not to bend to urban demands.
Thai academics call it ''the diseconomies of agglomeration.''
What may be just as urgent a problem is Bangkok's ''sinking feeling.'' City wells drawing water out of the mud base are dropping the land by some four inches a year. During rainy periods, some city streets are flooded for days. Unless costly new water supplies are found and more canals dug, the city could be below sea level by the year 2,000.
With some 5 million people in Bangkok now, the government hopes to cap the population at just over 8 million by 1990. Then it hopes peasant drift to the city will be reversed. With foreign assistance, eight ''secondary'' cities are being developed. Over 3,000 ''illegal'' factories are listed for removal. An elevated expressway being built over the city center to relieve traffic congestion is nearing completion, and an elevated rail line has been approved. Also, trucks are banned on city streets during daytime.
Such measures are to buy time until the biggest alternative to Bangkok is developed, sometime in the 1990s. The Eastern Seaboard Project, as it is called, ''is our only hope,'' says the planning board's assistant secretary-general, Dr. Phisit Pakkasem.
It may also be the launching pad for Thailand's takeoff as an industrial country.
Along the coast of the Gulf of Thailand, about one to two hours' drive south of Bangkok, the government plans to use the natural gas now coming onshore to build a job-creating industrial complex that will, it is hoped, check the growth of Bangkok.
A $5 billion investment in rail, water, roads, ports, and other facilities by 1985, plus 14 semiprivate projects such as soda ash, fertilizer, steel, and various petrochemical plants, will rely on the abundant gas reserves offshore. Initial plans call for at least 700,000 new settlers near the towns of Laem Chabang, Sattahip, and Rayong.
Sattahip, a former US naval base now used by the Royal Thai Navy, will be opened first for port traffic, with a deep-water port planned at Laem Chabang for agricultural products and light industry.
Besides serving as an alternative to Bangkok, the Eastern Seaboard Project could, potentially, spearhead development into Thailand's poorest region, the northeast, near Kampuchea (Cambodia). A $300 million gas separator plant expected by 1985 will produce 463,000 tons of cooking gas a year -- mainly for rural use -- plus 340,000 tons of ethane. A second separator by 1990 would be needed to meet the expected demand of 856,000 tons a year for cooking gas. The gas is usually compressed and bottled for sale to consumers.
A $590 million gas-based fertilizer plant, to be built by a Swedish firm, will also go directly to help farmers boost productivity.
Will the people come? Officials know that universities, government offices, and urban ''bright lights'' are often more of a draw than just jobs.
''We don't want to build another Braslia,'' says Dr. Sawit Povihok, director of the project.
Another limit may be water. The area is dry and sandy. Many reservoirs and pipelines are now being built. But it may not be enough. A dam some 60 miles to the north on the Bang Pakong River may have to be built.
Smack in the middle of the project lies Pattaya, now the most popular tourist lure outside Bangkok, known as the Thai Riviera. Last year over 1 million visitors stopped last year at this resort. The potential pollution from the new industries has many officials worried about the effect on Pattaya.