Colombo, Sri Lanka — It was not a typical ambush site - a hairpin turn in the mountains, a narrow bridge crossing a ravine. It was a flat stretch of road in an upper-middle-class neighborhood on the outskirts of Jaffna, where the Tamil homes are well appointed, adorned with the sacred cows of Hinduism, in gilded statuary.
The ambush party - 14 ''Tamil Tigers,'' armed with Soviet-made rifles and grenades - attacked the jeep-riding soldiers with precision, on three sides. They received active support from many affluent Tamils of the neighborhood. As always happens, the guerrillas disappeared after the ambush.
The July 24 ambush, in which 13 soldiers died, was the immediate catalyst for the bloodshed that recently gripped Sri Lanka for 10 destructive days. (Tamil partisans claim that the ambush itself was in retaliation for an incident the week before. It is said Sri Lankan soldiers raped several Tamil girls from the Palaly Training School near Jaffna the week before. The victims are said to have committed suicide.)
More broadly, however, the violence on both sides has reflected deeply rooted suspicions between the Sinhalese, who are mainly Buddhist, and the Tamils, who are largely Hindu. Since Sri Lanka's independence in 1948, the confrontation has centered on the question of either autonomy for the island's 18 percent Tamil minority or an independent state. The sentiment for independence appears to have grown in recent years and especially since the latest strife.
As the central government has failed to come to grips with Tamil concerns of political disenfranchisement, the influence of moderate groups, including the just-banned parliamentary party, the Tamil United Liberation Front, has begun eroding. And the underground Tigers appear to have gained popular support following the recent Sinhalese-Tamil upheaval.
Both government officials and military intelligence sources concede that they have little information on the Tigers. As a small and highly disciplined cadre of terrorists from the north, the Tamil Tigers, since 1975, have been adding a measure of violence to demands for an independent state.
They are believed to have expanded into the Eastern Province. And the government fears that they have forged an alliance - short-lived as it may be - with urban guerrillas of the now-banned People's Liberation Front, a Sinhalese Marxist group which launched a bloody and abortive insurrection against the government in April 1971.
Even before the latest violence, the Tigers had displayed growing confidence over the last 18 months. Recent events are likely to have enhanced Tamil support for them.
According to a Sri Lankan Army officer just returned from the north, the Tigers are recruiting angry young men among the refugees of Colombo as soon as they get off the boats in Jaffna. Tamil partisans argue, however, that the Tigers' strict discipline - reportedly they are not permitted to marry and may not smoke, drink, or use drugs - and highly secretive organization requires them to be very selective in their recruitment.
With a hard-core membership believed to number 500, the Tigers are mostly men in their 20s, weather-hardened and tough. Some are from the fishing villages of the northern peninsula, but others are middle-class student activists who have been alienated by what they feel is discriminatory treatment in Sri Lanka's university system.
The elusive Tigers strike with impunity, then go to ground. The Army recorded 60 Tiger incidents in 1983 - ranging from political assassinations and ambushes of army patrols to bomb attacks and acts of sabotage. Yet they have not arrested one Tiger or recovered one body after an attack.
The Tigers' international connections allegedly range from the Palestinians and India, to Israel, Libya, and Iraq. But military intelligence sources concede privately that the government just does not know, though it believes that the main financial support of the Tigers comes from smugglers on the north coast of the island, and from Tamil remittances from abroad, especially from India's Tamil-majority state of Tamil Nadu, which is only a few miles away across the Palk Strait. The Tigers may also support themselves by robberies.
Well trained enough ''to fight an army,'' the Tigers are becoming more politically sophisticated and adept. When they called for a boycott of municipal elections in the island's northern, Tamil-majority districts in May, up to 95 percent of the electorate stayed away in many areas.
Today, there are 1,300 troops in the Jaffna area - the disputed Tamil homeland now under virtual occupation by an army of southern Sinhalese. The military has embarked on a ''pacification'' program. The primary goal of their ''search and destroy'' missions is to ferret out the Tigers now deeply underground.
Spearheading the military offensive are the Raja Rata Rifles, an elitist, yet very undisciplined force whose members have mutinied at least twice since May 18 - once in Jaffna and once at their headquarters in Anuradhapura in central Sri Lanka.
On both occasions, their wrath was turned against the beleaguered Sri Lankan government, charging that its Tamil policy was far too soft.