Namibia: Realism Key for Economy. Guerrilla Incursion Increases Doubts about SWAPO's Political and Economic Savvy. SURVIVING WITHOUT SOUTH AFRICA

GORDON MERRINGTON remembers all too well what happened after the revolution in neighboring Zimbabwe.

A North Korean political commissar was assigned to the office of Mr. Merrington, a housing specialist. His job: to monitor Merrington's telephone calls - even though he didn't speak a word of English.

"It was a total waste," recalls Merrington, who now lives in Namibia. "It seems every time a liberation group takes over a nation, they feel obliged to remake the economy. I just wonder if we're going to have to reinvent the wheel here, too."

His is a legitimate worry. For on April 1, this southern African territory started down the road to independence after almost 75 years of South African rule. That's when a plan took effect for a United Nations-supervised transition to elections in November.

But then hundreds of guerrillas from the South West Africa People's Organization (SWAPO) allegedly came charging over the border from Angola. At least 300 rebels and members of South African- backed security forces died in the clashes, which ended with a cease- fire arranged last Sunday. Under the plan, SWAPO fighters are supposed to gather at designated assembly points to be escorted back to Angola by the UN and confined to bases there.

Analysts reckon the incursion either was a terribly miscalculated attempt to set up bases here - thus violating the UN accord - or the work of a breakaway faction. (SWAPO claims its soldiers already were here and were fired on by security forces.) Either explanation raises questions about whether SWAPO, the group most likely to win an election, has the coherence and savvy to run the place - especially the economy.

For analysts warn that while SWAPO will inherit a workable economy, it will have to do some sophisticated and unrevolutionary things to keep it that way. As a start, it will have to tread lightly around South Africa, which controls vital transport routes. Last week's battles showed Pretoria's willingness to come down hard on those its deems threatening.

SWAPO also will have to take care not to scare off the country's whites, with their needed skills and capital. That means no radical tinkering with the economy. For the stakes, analysts say, could not be higher: a matter of making this place a Botswana - southern Africa's showpiece of economic stability - or a basket case.

"If the ruling party goes for an orthodox Marxist orientation, we'll go down the drain," says Fanuel Tjingaete, a University of Namibia economist. "If it's realistic, we'll survive."

Compared with the sorry state of many of its African neighbors, Namibia has a lot going for it: great mineral wealth; South African- built roads and rail lines; relatively few people to feed (about 1.5 million). The UN has trained 2,000 bureaucrats for the new nation at a SWAPO school in Zambia. And scores of Namibians received college educations on foreign scholarships - a far cry from the handful of university graduates nearby Mozambique boasted, for instance, when Portugal pulled out in 1975.

But what SWAPO inherits could stymie even the most experienced of governors. The economy grew an average of only 1 percent per annum from 1971-85, mainly due to drought and a drop in world prices for base metals and minerals - the country's big cash earners. …