Mah jong and cards are losing ground to playing the stock market as the most popular form of gambling here, the market is booming and speculators are having a ball.

From $200,000 a day just last year, the daily volume has rocketed to $37 million. Some market analysts fear a crash is just around the corner, but most believe the boom will last.

Besides doctors, lawyers and rich merchants, the market is attracting a large number of wealthy housewives. "Many of these women now come to bet on the market instead of playing cards with their friends or going to morning fashion shows," commented a U.S. investment banker. "It's a fad, of course, but a lot of people are making a lot of money."

To draw this crowd, several brokerage houses have decorated their offices at great expense. Thap Securities Co., Ltd., an affiliate of New York's Bankers Trust Co., has hung an impressive collection of modern oils by Thai artists and installed rows of comfortable leather couches.

The atmosphere is vaguely reminiscent of a sedate casino. Waitresses in blue uniforms circulate, passing out soft drinks and snacks. Scores of heavily jeweled women and a few retired businessmen watch raptly as an attractive young woman chalks up fluctuating prices on a big white board, taking her cue from a loudspeaker.

At the other end of the speaker is where the real action is, in the jammed trading room of the Securities Exchange of Thailand. Although the SET lists only 31 companies, its trade volume has made it one of the largest stock exchanges in Asia, bigger than those in Hong Kong, Singapore and Sydney.

With binoculars in one hand and openline telephones in the other, about 200 youngmen and women keep a constant watch on the big board and deliver running accounts to their offices. Television cameras trained on the board relay the fluctuating prices to closed-circuit TV sets in the trading room windows where passersby crowd around in buzzing clusters.

But the military junta which seized power last month has just announced a package of tax reforms intended of convince more private companies to go public and, perhaps more important, to cut down on the rampant speculation which has pushed the market to its dizzy heights.

The reforms, which have not been spelled out in detail, also are likely to erode the extremely attractive investment tax. Current legislation leaves tax-free the first $500, 30 per cent of the remainder and all capital gains.

Furthermore, until recently, most brokers did not require buyers to put up any cash at all. "So, it was very common for people to get in, make a quick profit and get out without ever showing a single that," said Sivaporn Dardarananda, managing director of Thai Securities Co., Ltd.

Now, Thai Securities requires all new customers to put up one-thind of their purchase price, similar to practices in New York and other major Western markets, he said. The impending changes in legislation also are expected to cut down on quick in-and-out trading by taxing short-term capital gains.

Sivaporn, who said he and other brokers had done "seven years of ground work" leading up to the present boom, conceded that the majority of Thai investors were still "terribly unsophisticated." But, he said, brokers were continuing to hold lectures among wealthy clientele and "we should soon reach a time when genuine investors, rather than speculators and gamblers, dominate the market."

A major factor in whether this happens will be whether those with funds to invest develop greater confidence in the new Thai regime than has been the case in the last three years, several market analysts said.

They noted that the majority of investors are Sino-Thais, with family and business links among the overseas Chinese communities of Southeast Asia. "This means that the profits tend to circulate throughout the region," said one American investment banker. "Very little is being plowed into development projects in Thailand. And unless that kind of investment takes a turn upward pretty soon, I'm dubious about the long-range outlook here."