If the odd coup scare, inflation, pollution, rising crime and other urban ills are not enough to dampen Thai New Year spirits, Bangkok residents have another reason for feeling low these days.

Their city, quite literally, is sinking, and experts are growing alarmed.

The problem is relentless use of underground water, which causes the level of the land above it to drop. Already the proliferation of wells for residential, commercial and industrial uses has caused parts of the Thai capital to sink below sea level, cracked buildings and aggravated a serious flooding problem during the rainy season.

Now a team of specialists is winding up three years of research into the problem, and the government is expected to consider its proposals shortly.

Basically, the proposals revolve around one central goal.

"We have to stop people from pumping ground water," says Prinya Nutalaya, a member of the research team. "If nothing is done, and at the present rate of pumping, Bangkok will be completely below mean sea level in 20 years." Within two or three years, he said, the city would have to build major dikes to control more frequent and severe flooding. Some temporary dikes already have been built, Prinya said.

Prinya, a professor at the Asian Institute of Technology here, compared Bangkok's problem with that of Venice. The Italian city had been sinking by one to two centimeters (about a third to three-fourths of an inch) a year until authorities solved the problem about five years ago by stopping the pumping of ground water, Prinya said. In Venice's case, he said, it was also necessary to grout certain valuable buildings damaged by the years of land subsidence, as the sinking is called.

While the cause of Bangkok's problem is the same, the Thai capital is far worse off, Prinya said. The eastern parts of the city have been sinking by about 10 centimeters (nearly four inches) a year since 1978, and one area recorded a drop of 14 centimeters, or 5 1/2 inches) a year.

Since benchmarks were first established in Bangkok in 1939, Prinya said, the most severely affected parts of the city have sunk by about one meter (39 inches). Now the rate of subsidence is accelerating, he said.

Although other cities have sunk much more than Bangkok over the years--Mexico City and Tokyo, for example--this capital's geography gives it a special problem. Never very high above sea level to begin with, the city has long relied on a network of canals called klongs to carry off surface water and control flooding. The klongs have also been used for transportation.

In recent years, however, authorities have filled in many of the klongs to make new streets or widen existing ones. One result has been to make many parts of this city of 5 million people more susceptible to floods. Thus during the summer rainy season, klongs overflow, many houses and shops are waist-deep in water, and it is literally possible to fish in some streets.

According to Prinya, the sinking of Bangkok can be arrested by halting the use of underground water, but there is no way to bring already sunken areas back up to their former levels.

As a first step toward halting the process, the research team wants the government to divide the capital into zones in which the use of wells would be regulated according to the severity of the subsidence.

The study group, under contract to Thailand's National Environment Board, has proposed banning new wells in the worst-affected areas, phasing out the use of ground water by the Metropolitan Water Works Authority and charging owners of existing wells for water usage at a rate of one baht (22 cents) per cubic meter.

Currently the municipality pumps out 30 percent of the 1 million cubic meters of ground water extracted daily in the Bangkok area, Prinya said. The rest of the municipal water supply comes from surface water. There is now no charge for water drawn from the metropolitan area's 10,000 private wells.

Although assessing charges would not address the immediate problem, and the government would have to install gauges in all the wells, Prinya said this measure would "make people think twice before pumping ground water" and allow the government to enforce further restrictions in the future.

Part of the problem is that the city government's water distribution system has not kept up with private sector expansion, Prinya said. Thus businesses and industries in outlying areas have been obliged to sink their own wells.

The U.S.-trained geologist said a committee currently was looking into expanding the use of surface water to make up for prohibitions against pumping ground water. He estimated it would cost $200 million to $300 million to build a surface water system to meet needs currently supplied by wells.

Another possibility is to "recharge" underground reservoirs by pumping surface water back into them. This could spare some of the expense of an expanded distribution system but would still require treatment and water quality control facilities.

In any case, Prinya said, "something must be done" to stop Bangkok from sinking. "There is no other solution unless we keep building dikes."