Bangkok — Multicolored opium poppies are in full bloom on the steep hillsides of northwest Thailand. A new opium war is being fought there against the private army of Khun Sa, ''king of the golden triangle.''
Soon the petals will fall, and two or three weeks later the resinous raw opium in the flower pod will be ready for harvesting.
Although illicit opium production is tolerated for a variety of social, political, and economic reasons, the campaign against this Burmese warlord, allegedly the biggest manufacturer and seller of heroin in Southeast Asia, indicates that Thailand has adopted the tough narcotics policy President Reagan has been urging on Bangkok for the past year.
''Government pressure on Khun Sa from both Thailand and Burma should produce a significant decline in the availability of narcotics around the world,'' says a Thailand-based narcotics expert, although there is disagreement on just how big an impact the campaign will make. Whether the pressure will continue and produce permanent declines in availability of heroin remains to be seen.
Certainly the military operation against Khun Sa's Shan United Army (SUA) is one of the most vigorous and determined actions against narcotics that Thailand has ever carried out.
The Thais appear prepared to suffer casualties. So far they have lost 24 killed and about 60 wounded in savage clashes in mountainous jungle where even mules find it tough going.
The SUA has reportedly lost approximately 80 killed and 200 wounded. Another 180 supporters have been taken into custody.
Khun Sa and the bulk of his army are believed to be on Burmese territory, but he has vowed to make retaliatory attacks and the Thais are preparing for them. Reinforcements arriving at weak points on the border include volunteer rangers from local villages.
The Thais are disappointed that they found neither opium nor heroin in Khun Sa's strongholds, located in the ''golden triangle'' bordering Burma and Laos. But the narcotics police chief, Gen. Pow Sarasin, claims that the operation reduced the area's potential for heroin production by half.
Foreign narcotics agents question that estimate but say Khun Sa's drug empire has suffered a serious setback.
His control and financing of distributors and the network itself have been interrupted and the movement of opium from the impending harvest to the drug king's refineries made more hazardous.
Consequently, smaller supplies of heroin from the ''golden triangle'' are expected in the outside world during the next year.
The agents and foreign diplomats are also heartened by the new cooperation on suppression between Bangkok and Rangoon. The Thai foreign minister visited Rangoon immediately before the military action, and other officials will be going there very soon for more coordination talks.
Part of the problem involves the loyalty of local Thai people, who feel neglected by Bangkok. Without their support, the government can never stamp out the drug-dealing army.
Local officials say Khun Sa has been able to recruit 1,000 men from Thai border villages since the fighting began. One reason is that he is able to give his supporters a higher standard of living than that of other local people.
When Thai forces captured his base at Ban Hin Taek, 20 miles inside Thailand from Burma, they found that the ramshackle village of a few years ago had been transformed into a modern town.
More than 300 well-built houses replaced bamboo-and-leaf huts. (Khun Sa's own house had a swimming pool, electric fans, color television, and a video recording machine with a supply of foreign movies.)
A 100-bed village hospital contained modern equipment, and a new electricity generating plant had just been installed to give power and light to the villagers. Wooden posts had been raised to carry power lines.
A new icemaking plant was another modern amenity made possible in this extreme remoteness only by the enormous profits of Khun Sa's drug empire.
No Thai official has yet explained why action was delayed so long when Khun Sa had been known for years to be running his empire on Thai territory.
The half Chinese, half Shan (a Burmese tribal minority) warlord himself has said he brought his army into Thailand to escape Burmese suppression. He has claimed they have been fighting 20 years for the liberation of the Shan people.
His supporters say he has placed that struggle above all other things, including the interests of his own family.
He has nine children, among them a daughter said by Shan people in Bangkok to be studying in the United States.