BURMA'S sundry ethnic groups have battled so long that last year's outbreak of war in this divided and isolated nation could have easily drawn scant attention. After all, 40 years of civil war may be a 20th-century record. But the fighting that erupted last September between government troops and the largest rebel group, the Karen National Union (KNU), has ricocheted into international circles as it has intensified.
In April, the government claimed ``the backbone of the KNU has been broken'' after it took the rebels' best defended stronghold, a place called Myawaddy, about 170 miles from Rangoon.
The once-hermit-like government has started to give regular reports of rebel clashes, even revealing casualty numbers.
But the KNU received a boost on May 9 when United States Sen. Patrick Moynihan (D) of New York spoke out on the rebels' behalf. The war needs international mediation, he said.
Last month, Thailand offered to mediate between the Rangoon regime and the KNU. Such talks seem unlikely, however.
Any outside interference that might give the rebels some sort of world recognition is a red flag to the current regime. The Army regards itself as the guardian of national unity.
A series of rebuttals to Senator Moynihan was carried by Burma's sole newspaper, the official Working People's Daily.
Both the KNU and Burma's Army, which is dominated by majority ethnic Burmans, have been willing to suffer hundreds of casualties. Each side appears determined more than ever to tip the political balance, with unusual help from foreign powers.
``We're seeing a besieged regime trying to prove its worth to Burmese,'' says a Rangoon-based Western diplomat. The KNU, he adds, is on the attack to take advantage of the regime's increasing unpopularity. Both sides appear to be putting their all into the showdown.
Short of manpower, the 170,000-member Army has lately begun to round up idle citizens on the streets of the capital to serve as porters in the jungle warfare.
``They've run out of rural people to be porters,'' says another diplomat. For the Karen, a hill tribe of about 2 million, the recent battles may have reduced its estimated 6,000-member fighting force by about 10 percent. KNU guerrillas also lost three key military strongholds in their homeland near the border with Thailand.
The KNU is just one of about 10 non-Burman guerrilla groups whose combined forces are estimated to be about 20,000 to 25,000. Most of these minorities have sought to secede from the Burman-dominated government. But in 1987 their leaders declared a goal of seeking only limited autonomy within a federated Burma.
This loose alignment of ethnic minority groups, which control vast, remote areas of Burma, obtain arms through their control of black markets, smuggling, or opium-growing. Various attempts to negotiate ethnic harmony since 1948, when Burma became independent, have failed.
Last August and September, hundreds of student-led protesters who demanded democracy and an end to economic decline were killed in the streets by the military. When martial law was imposed on Sept. 18, with Army chief Gen. Saw Maung designated as nominal leader, thousands of students fled to border areas, especially Karen territory, where they sought arms and help to overthrow the regime.
To quell political unrest, the regime has tried to reverse its unworkable socialism, allowing free trade and opening the country to foreign investment. The first nation to grab the chance to exploit Burma's rich forest and fishing resources was neighboring Thailand.
All these rapid changes provided the political momentum for a renewed conflict with the KNU. With Burmese students on their side, the KNU stepped up attacks, believing the military was weakened by the need to deploy troops in cities.