BANGKOK, Thailand — As an up-and-coming young Thai professional during the mid-1980s, K. Surapong regularly ended long workdays with a few drinks with his buddies and sex with prostitutes--sometimes protected, often not.

Surapong, now with full-blown AIDS, has spent the last few years as one of the country's leading "guinea pigs," testing an array of drugs that temporarily arrest the symptoms of the virus.

"I promised my doctor I would help him to the last day of my life," said Surapong, the first Thai to test a variety of antiviral drugs, including AZT. At 38, he is physically a shell of his former self, and does not expect to see his 40th birthday.

The tragedy for Thailand is that Surapong's former lifestyle is still fairly common among Thai men, most of whom have their first sexual encounter with a prostitute working in the nation's thousands of brothels, coffee shops, massage parlors and other fronts for the sex trade.

Sex for cash here is not just recreation, but an integral part of the business culture. Thailand's prospering economy has created a boom in expensive executive clubs for business entertainment. Sex is prominent among the offerings.

Realizing the threat AIDS poses to one of the world's fastest-growing economies, Thailand's business community has begun to implement AIDS prevention programs in the workplace and is contributing to government AIDS programs.

"It's a very, very scary situation," said Chanin Donavanik, executive director of the Dusit Thani Hotel Group, Thailand's largest chain. Two years ago, the company launched an AIDS awareness campaign among its 6,000 employees, requiring attendance at three-day seminars and AIDS briefings as part of new employee orientation.

Although government statistics show only about 2,000 people actually sick with AIDS, estimates are that about 600,000 of some 57 million Thais are infected with the HIV virus. (Some officials believe more Thais are sick, but are not counted because they have left urban areas to die quietly in remote villages.) By comparison, the United States has more than four times the population, but an estimated 1.1 million people who are HIV-positive.

According to several studies, from 2 million to 6 million Thais--3% to 10% of the population--are expected to be infected by the year 2000. About half a million Thais are expected to have died of AIDS by then.