Thailand has mounted a concerted drive against its massive illicit drug trade and for the first time U.S. narcotics agents are convinced that the government means business.

Thai authorities are seizing record quantities of heroin and other drugs, arresting dealers and couriers, destroying jungle laboratories where opium is converted into heroin and striving to convince tribal opium farmers to grow legitimate crops.

The government is now studying U.S. conspiracy laws. Similar legislation here would enable authorities to arrest presently untouchable top figures in the drug trade. Police are currently restricted to arresting only suspects found with drugs in their possession.

The key to crushing the narcotics traffic in Thailand and the rest of Southeast Asia, according to a U.S. Drug Enforcement Administration source here, is to ensure cooperation between Thailand and its western neighbor, Burma.

"Once these two governments start working together in earnest," said the source, "we can pack our bags and go home."

Thai Foreign Minister Upadit Pachariyangkun visited Rangoon recently and, according to Thai anti-narcotics officials, returned with "an agreement in principle" to cooperate against the assorted Burmese rebel groups who finance their wars with the Rangoon government by smuggling heroin into Thailand.

"Even though the details are still to be worked out," said the DEA agent, "the rebels are already under pressure." He praised recently promoted senior Thai police officials for their efforts to squeeze the smugglers between Thai forces and units of the Burmese army.

The crackdown is a priority project of Prime Minister Thanin Kraivichien. He announced the drive within days of being appointed to office by military officers who staged a coup d'etat Oct. 6.

For years, a number of senior officers have been leading figures in the narcotics traffic. Until recently there were strong signs that, partly because of their irritation over Thanin's doggedness against drugs, they were planning to depose him. But the puritanical former Supreme Court justice seems to have survived the threat.

"We hope he's going to be around for a long time," said a DEA source. "He's the first Thai prime minister who's been serious about drying up the drug trade. We're highly impressed with him."

The DEA works closely with Thai narcotics agents. Heroin produced from opium grown in the "golden triangle" region of northern Thailand and neighboring Burma accounts for some 30 per cent of the illegal drug consumed by U.S. addicts.

The bulk of heroin reaching U.S. streets comes from Mexico. U.S. and Mexican authorities are waging an intensive war against this traffic and the DEA here believes that Southeast Asian traffickers are stepping up their pace to fill the gap.

"The heroin trade in Southeast Asia will never be dried up completely," DEA regional director Daniel J. Addario said in an interview. "But we believe that the Thai government is deadly serious about doing its best and that the flow can be slowed down to a trickle."

This optimism is a far cry from DEA attitudes only a year ago. The United States was then alone in pressuring Thailand, with little effect. Now, Canadian, British, French and Dutch agents have begun to work with the Thais because of the sharply increased flow of heroin from here to their countries.

U.S. agents here welcome the arrival of colleagues from other Western countries because, they believe, pressure from all those countries plagued by addiction and drug-related crime will help keep the Thai government on the move against traffickers.

Police Gen. Pao Sarasin, deputy commander of the criminal investigation bureau, noted that Thailand has its own reasons for the crackdown. "Right now, we have at least 300,000 addicts in this country, and perhaps as many as 600,000," he said in an interview. "And as the number of addicts rise, so does crime."

Perhaps more important in providing high-level government pressure on police and customs authorities, a rapidly escalating number of children of influential Thais are becoming addicts.

A similar development has alarmed authorities in Burma, where a son of President Ne Win is among the addicted children of powerful Burmese.

In Thailand, "fully 50 per cent of our addicts are between the ages of 14 and 25," Pao said.

The grade of heroin available to local users is so high that drug-induced deaths, particularly among young people, are soaring. "Thai addicts can buy heroin which is 90 per cent pure," Pao said. "In the United States and Europe it's usually cut to no more than 3 to 5 per cent."

Ironically, Pao said, by reducing the flow of heroin to the West, Thailand is increasing its own drug problem. "We're helping many countries by holding drugs back, but the result is that it stays here, prices fall and more and more Thais are becoming addicted."

The officer appealed to the United Nations, which runs an experimental crop substitution program in the opium-growing areas of northern Thailand, to increase funds to this country. He noted that the U.N. program, which is to end next year, was funded with $2.5 million, while similar programs in Burma and Pakistan have been granted over $6 million apiece.

PAO denied that top-ranking military officers were involved in the drug trade, "although some of them may have been in the past." A DEA source confirmed the claim, "As far as we know," the source said, "no Thai officer has been involved since Oct. 6. The word has come down from the top." A civilian trafficker was recently executed.

Nevertheless, the kingpins of the trade, usually businessmen with legitimate fronts, are still at large. "Our law was enacted in order to protect the innocent," Pao said, "but it ended up protecting the guilty."

He said a special committee has been appointed to study the U.S. conspiracy laws and he anticipated similar Thai legislation would be adopted "very soon." This would empower authorities to arrest suspects fingered by couriers, middle men or anyone with any evidence linking a seemingly legitimate businessman to drugs.