While two parched years of drought have withered the production of virtually every food crop in southern Africa and played havoc with the fragile economies of a half dozen nations, one crop is thriving as never before.

The hardy tobacco leaf, Zimbabwe's golden weed, is heading toward a year of record harvests and prices. By year's end, farmers here will have exported nearly 90,000 tons of tobacco to 55 countries at a gross value of $240 million.

That means tobacco alone will provide nearly 20 percent of this country's foreign exchange, an item as scarce here as rain. It makes Zimbabwe Africa's largest tobacco producer. And it gives the tobacco industry--the growers, packers and cigarette manufacturers--political clout that might make farmers back in Virginia or North Carolina green with envy.

There are no government- imposed warning labels on cigarette packs or bans on advertising, and no one in or out of government has even considered an anti-smoking campaign.

Even the vice chairman of the Zimbabwe Cancer Association, Dr. Joseph Barkley, is quick to concede, "I just don't know what this country would do without tobacco." Farmers also don't have to worry about government regulations: Tobacco is the only major crop in Zimbabwe that is sold at a free auction market with no price controls. The only quotas are those set by the growers themselves to keep their product in demand and prices high. And while the cigarette market in the United States and other western nations shrinks annually, cigarette sales here climbed 16 percent during the past two years.

Despite the government's often stated commitment to socialism and racial equality, no one appears to want to tinker with the tobacco industry's profits, nor with its virtually all-white complexion. In fact, the government itself could be said to be in the cigarette business, since last year it took 79 percent of the profits, or $17.5 million, in excise and corporate income taxes from one local cigarette manufacturer alone, Rothmans of Pall Mall.

"There's no question tobacco is the main crop that has kept our farming industry in business this year," said Minister of Agriculture Denis Norman, himself a part-time tobacco grower. "It's a real winner for us."

Not everyone shares Zimbabwe's enthusiasm for the golden leaf. The World Health Organization has launched an international antismoking campaign charging that, besides its debilitating health effects, tobacco consumes large quantities of land, capital and labor in the Third World that could otherwise be devoted to producing sorely needed food supplies.

WHO has also condemned what it calls the "hidden costs" of tobacco farming: the reductions in diet for low-income people who spend money on cigarettes rather than food and the large numbers of trees cut down to burn for smoke to cure tobacco. The organization estimates that 12 percent of the trees cut down each year worldwide are used for tobacco curing.

But even the United Nations expresses mixed feelings about tobacco. While WHO excoriates the "killer weed," the U.N.'s Food and Agriculture Organization encourages its cultivation as one alternative for small-scale Third World farmers desperate for cash.

Zimbabwean officials reflect the same ambivalence. In a speech last week, Minister of Health Oliver Munyaradzi denounced the growing of cash crops such as tobacco instead of food as "one menace we must guard against. In our one-track dedication to the earning of scarce foreign currency and our almost suicidal dedication to providing primary goods to the developed world, we in the developing countries unwittingly neglect our basic interests."

But the strong rhetoric yields little action. That is because the tobacco industry directly employs 90,000 farm owners and laborers, according to industry spokesmen, and because government itself takes 39 cents in taxes on every pack of 20 cigarettes sold.

"The government recognizes the importance of tobacco even as it milks it," said a spokesman for the Tobacco Industry Council here. "The fact is, if you took out tobacco, it would be traumatic for the entire economy, and government is aware of this no matter what they might feel. They're stuck with the fact that what's good for tobacco is good for Zimbabwe."

For years tobacco was both the beginning and end of agriculture here. Farming diversified during the days of white-ruled independence when a worldwide boycott forced the former British colony, then called Rhodesia, to grow most of its own food. But tobacco remained agriculture's backbone, and it still is.

"This town was built on tobacco proceeds," says Agriculture Minister Norman about Harare. "Tobacco paid off everything. That's what brought me to this country 35 years ago , and it brought hundreds of others as well."

Then, as now, about 95 percent of the tobacco crop was sold for export. During the days of economic sanctions, the industry did not stop exporting, but it was forced to go underground.

"Nothing was impossible," recalled R.G. Newman of the Tobacco Marketing Board. "We got a lot of it out through South Africa and Mozambique then under Portuguese rule . There were plenty of countries who denounced us publicly while buying from us under the table. But I wouldn't want to go into detail because it would embarass some of our best customers."

Despite the best efforts of the clandestine marketeers, tobacco's share of the economy dropped during the boycott years. A post-independence glut also kept prices down during 1980 and 1981, and government price incentives to maize growers convinced many farmers to forsake the golden leaf for food crops.

Where 3,000 commercial farmers--virtually all of them white--once grew flue-cured tobacco, now only 1,300 do. There are also nearly 4,000 growers of the less abundant burley tobacco, most of them blacks, but even here the 155 white growers account for 65 percent of the product.

The drought has dramatically changed all that. Food crops have been shrunk by two years of poor weather, while tobacco, which can grow in poor soil and with little rain provided it comes at the right moments, has thrived. The golden leaf, which three years ago trailed gold, ferrous metals and chrome as an export commodity, this year has returned to the top of the list.

Political influence is a natural byproduct of that position. When the industry learned that the U.N. Center on Transnational Corporations was planning what industry sources feared was a hostile study of tobacco in Zimbabwe, Thailand and the Philippines, it made certain that a sympathetic official from the Ministry of Agriculture was assigned to the study and that he was thoroughly briefed by the industry, the sources said.

"The ZTA Zimbabwe Tobacco Association goes up and down to the minister of agriculture like a jack-in-the-box," said one industry member. "It's traditional."

The Tobacco Industry Council, the umbrella group made up of growers, packers and cigarette manufacturers, has hired a retired senior civil servant, M.G.B. Rooney, as its lobbyist and spokesman.

He said he prefers the low-key approach.

"We don't get on rooftops and tell everybody to smoke," he says. "I have connections with my former colleagues in government. The council members talk to the ministers and I talk to the senior civil servants."

Rooney sees his job as preventive medicine: to keep an antismoking campaign from ever getting started.

"We're trying to keep one step ahead," he says. "We want to be ready for them when they come."