EENHANA, NAMIBIA -- Two black insurgents press their bodies against the scrawny scrub tree for cover as a helicopter gunship circles overhead, gradually tightening its orbit while a door gunner strains to catch a glimpse of the slightest movement on the Angolan border rushing beneath him.

On the ground, white South African soldiers, following telltale footprints in the fine sand, close in on their quarry.

A Buffel armored vehicle lumbers behind the soldiers. A short burst of AK47 rifle fire from the tree is answered by a stream of fire from the Buffel, and then there is silence as the platoon leader radios his base for body bags.

This brief and deadly drama, described by the pilot and ground troops, is repeated hundreds of times annually, as one of the world's longest continuously sustained guerrilla wars -- between the South African Army and the Southwest Africa People's Organization (SWAPO) in northern Namibia and southern Angola -- approaches its 21st anniversary.

In a sense, it is a forgotten war, lost in its sameness, and blurred in the consciousness of a world plagued by similar conflicts on almost every continent. It rolls on as Namibia, which has been administered by South Africa since the Germans were routed from South-West Africa in World War I, gropes toward independence.

The cost in lives and resources has been large: an estimated 10,000 SWAPO guerrillas dead in the past 10 years alone; uncounted civilian casualties on both sides of the border; nearly $1.5 million a day spent to maintain the South African military machine here; and inestimable property losses and monetary drain from the dislocation of the economy in Namibia and Angola.

The South African Army command does not disclose security force casualties, but authorities in Pretoria have announced the deaths of at least 30 servicemen this year, compared with last year's total of about 60.

After all the expenditure of lives and resources over more than two decades of conflict, neither side can claim victory. South Africa is no closer to closing the book on this war than SWAPO is to installing itself in the capital of Windhoek as the leader of an independent Namibia.

At best, South Africa can only say that through grinding attrition it is blunting the ability of SWAPO's military force to carry out the kind of spectacular cross-border attacks that were common 10 years ago. For its part, SWAPO can only claim that it holds Africa's mightiest military power at bay while engaging freely in what amounts to little more than armed propaganda.

Running parallel with the war, at a glacial pace, are efforts by the multiracial transitional government in Windhoek to hammer out a constitution that could lead to independence for the Texas-sized territory, whose population of 1.2 million includes only 100,000 whites.

Mired for four decades in international bickering and South African intransigence, the independence question has been complicated by the U.N. General Assembly's insistence that SWAPO is the "sole and authentic representative" of the Namibian people -- a position that is unacceptable to Pretoria.

However, South African military strategists in the field and at headquarters in Windhoek say they are winning the war along the 1,000-mile-long frontier. And although SWAPO denies it, there is evidence to support that assertion.

In 1968, SWAPO's total strength was estimated by South African military intelligence at 16,000; today, the estimate is 8,700. Because of its commitments to fight alongside Angolan and Cuban troops against South African-backed UNITA rebels inside Angola, it can field barely 800 men close to the Namibian border, according to South African military intelligence officers.

By contrast, the South African Army says it has 10,000 to 12,000 men under arms in Namibia's operational area, 65 percent serving in the South-West Africa Territorial Force and 80 percent of them black. Including South African Police Counterinsurgency (COIN) units and home guards, the total is said to be about 30,000.

SWAPO claims that South Africa has more than 100,000 troops on the border.

In 1980, at the height of the war, SWAPO combat units of more than 200 guerrillas regularlycrossed the porous border for sustained operations inside Namibia.

Today, the South African Army estimates that only about 60 guerrillas are inside Namibia at any given time and that they rarely stay for more than two or three days.

In 1980, there were 1,175 incidents reported by South Africa as terrorism, including intimidation of civilians. Last year there were 476, most of them confined to the 220-mile-wide Ovamboland tribal territory in north-central Namibia, and most of them relatively brief mortar and rocket attacks that resulted in few casualties.

There is no way to confirm independently the South African statistics, which SWAPO officials dismiss as being skewed to create the impression that the South African Army is winning the war.

"Today, after more than 20 years of struggle, SWAPO does not have the capability of penetrating more than {37 miles} across the border and sustaining a presence for more than six or seven days at the most," said Army Col. As Kleynhaus, a senior intelligence officer in the Windhoek headquarters.

"They are losing the support of the people, which they must have to sustain a presence inside. That's why they are concentrating on low-risk sabotage and standoff attacks, which are not effective except for propaganda value," Kleynhaus added.

Closer to the front, at the Army's Sector 10 headquarters at Oshakati, 28 miles from the border, Maj. Jock Seaward, an Army intelligence officer, said the biggest blow to SWAPO came last year when it failed to launch its annual "typhoon" mass infiltration through Ovamboland and Kavango to the east toward the vulnerable white-owned farms to the south.

"That was the big slap in the face for SWAPO," Seaward said. "They need the typhoon infiltration to prove to everybody that the final year of liberation has come. If they can't activate the Kavango, they can't win the war, and they know that."

Even closer to the border, at the Army's 54th Battalion headquarters here at Eenhana, five miles from Angola, Maj. Derek Els scoffed at the two SWAPO attacks this year on his base, which traditionally sees much of the combat in the central Ovamboland sector. One involved a few mortar rounds that landed in the bush hundreds of yards from the camp perimeter; the other a "lucky shot" rifle grenade that landed in a mortar pit, slightly wounding two soldiers, said Els, second-in-command at the base.

But Els and his men expressed admiration for the guerrillas' ability to elude their pursuers. "If you don't have a vehicle, it's hard to get a kill. They can run for days, and we just can't keep up," Els said.

Moving from one kraal, or native thatched-roof compound, to another for food and water, the guerrillas are frequently endangered by the South African Army's network of local civilian informants, Army officers said.

Even though 96 percent of all SWAPO fighters are Ovambo tribesmen -- and in spite of near-constant intimidation of the local population -- civilians in Ovamboland are increasingly informing on the movements of guerrillas, Kleynhaus said. In 1983, he said, there were 64 cases in which civilians brought information to the Army that led to the capture or killing of guerrillas. Last year, he said, there were 1,211 such cases.

"The book says that time is on the side of the insurgent, but that is not so here. They could see time running out on them in terms of the support of the people," said Kleynhaus.

Already this year, military intelligence officers said, 611 SWAPO guerrillas attempting either to enter or leave Namibia have been killed by South African troops, compared to 694 in 1986 and 350 this time last year. The Army expects to get 250 more kills by year's end.

Seaward openly acknowledged that South African troops enter Angola "almost daily" to pursue guerrillas and conduct "follow-up" operations. But he said that in most cases, fleeing insurgents head to the nearest Angolan forces, knowing that international pressure will prevent the South Africans from engaging the Angolans or their Cuban advisers.

South Africa's long history of incursions into Angola, ending with the most recent major withdrawal in 1984, has had its effect on SWAPO.

The main SWAPO military headquarters and training bases are safely situated nearly 200 miles north of the Namibian border, and SWAPO leader Sam Nujoma only rarely ventures that far south from the capital of Luanda, according to military intelligence officers.

Most of the guerrilla force's key field commanders are headquartered far from the front, wary of South Africa's ability to pinpoint their movements in the south and launch hit-and-run attacks against them. This results in frequent breakdowns in communication between the commanders and the field units on the border, according to South African Army officers.

The South African Army's assessment of the guerrillas' increasing weakness was disputed by a SWAPO spokesman in an interview in Windhoek, where the group's political branch is permitted to function.

"Of course we cannot deliver the results until after independence, but the military attacks are not low-grade," said Anton Lubowski, claiming that SWAPO has shot down South African Army helicopters and staged successful attacks on the headquarters at Oshakati. He said that many successful attacks go unreported and that the South Africans almost never mention casualties among their black troops.

"In the next few years we will definitely intensify our armed struggle," said Lubowski, who described northern Namibia as "the most intensified military zone in the world, proportionally to its population."

SWAPO officials alleged that security forces routinely commit atrocities on both sides of the border, sometimes torturing civilians for information and often firing indiscriminately in villages.

The pro-SWAPO Windhoek weekly newspaper, The Namibian, in January published a photograph of a dead insurgent lashed to the outside of an armored vehicle that allegedly was driven around the town of Ondoba to intimidate local residents.

Although the Army command denied the allegation at the time, an officer at the 101st Battalion confirmed the incident. He said the inside of the vehicle had been filled with bodies of guerrillas and one dead SWAPO fighter had been tied to the outside for the trip to a mortuary.

Acutely aware that completely successful counterinsurgency efforts have been rare in the history of revolutionary warfare, South Africa's military strategists say they are resigned to fighting a low-grade guerrilla war for a long time to come.

"There is very little aggressiveness in their strategy," said Kleynhaus. "The conditions have to be 100 percent in their favor before they attack. But I don't think that they can afford to stop fighting. They would completely lose the people if they didn't have a bomb go off here and a power line go down there."

Still, SWAPO's presence is being felt in northern Namibia, lending prestige and legitimacy to the SWAPO political wing.

SWAPO guerrillas have been able to create a siege atmosphere in the border areas. Aircraft that fly into this remote base, for example, approach for the last 50 miles at treetop level, mindful of the three or four SA7 missile teams that SWAPO is believed to operate in the area.

Political cadres of two to three guerrillas each are known to be operating freely in Ovamboland, moving from one tribal community to another to hold meetings, distribute revolutionary pamphlets and attempt to politicize the local population and gain the logistical support that is essential for any successful guerrilla war. About half of Namibia's population lives in Ovamboland.

In response, the Army is engaged in an extensive social "uplift" program designed to win the hearts and minds of the local population.

In Ovamboland, that task has fallen largely to the mostly black 101st Battalion, which has launched agricultural and medical assistance projects and encouraged local civilians to build the scores of small businesses that are springing up in the territory's capital of Ondangwa. HISTORY OF A CONFLICT KEY DATES IN NAMIBIA'S QUEST FOR INDEPENDENCE 1920

The League of Nations places the former German colony of South West Africa under a South African mandate.

1947 South Africa refuses to relinquish its mandate after the United Nations replaces the League of Nations. 1969 The U.N. Security Council declares the South African occupation of Namibia illegal and calls for an immediate withdrawal.

1973 The U.N. General Assembly recognizes SWAPO as the "sole and authentic representative of the Namibian people."

1978 The Security Council passes Resolution 435 calling for South Africa's withdrawal and the holding of U.N.-supervised elections that will lead to independence.

1983 Namibia's national assembly is dissolved and a new interim government is installed. President Reagan links implementation of Resolution 435 to withdrawal of Cuban troops from Angola.

1984 Negotiations in Lusaka, Zambia, lead to the withdrawal of South African forces from southern Angola.

1985 A multiparty conference leads to the creation of a constitutional council, which is given 18 months to draft a new constitution. A new transitional government is installed.

1987 SWAPO leader Sam Nujoma reiterates his willingness to sign a cease-fire agreement with South Africa in order to implement Resolution 435. South Africa warns Namibia that steps taken by the interim government that "interfered with South Africa's international interests and undertakings are unacceptable." The interim government prepares its draft constitution for consideration by Pretoria.