Zimbabwe, regarded as the granary of black Africa just two years ago before the onset of the worst drought in its history, will have only a two-week supply of corn, the staple food, remaining by the time of the next harvest, according to the head of the country's major farmers' organization.

The southern African nation will have only 50,000 tons of corn in stock--half of what is consumed each month--by the end of next March, when the next harvest is due, said Jim Sinclair, president of the Commercial Farmers' Union, speaking today at the organization's annual meeting.

Agriculture Minister Dennis Norman, who visited the United States last month to seek food aid, acknowledged the accuracy of the figures, the first time the problem has been outlined so drastically in public. He said, however, that the normally food-rich country would have enough corn to avoid the embarrassment of having to import that item, at any rate.

Norman said the drought, unrest in the southwestern province of Matabeleland and fluctuations in farm prices and interest rates have brought agriculture, the mainstay of the economy, to a "low ebb."

Western diplomats regard a successful Zimbabwe as a key to the future of mineral-rich but economically poor southern black Africa.

Today's meeting of the predominantly white Farmers' Union was addressed by six Cabinet ministers, many of whom came under sharp criticism of government policy. Although the atmosphere was friendlier than that of the four previous sessions since black rule began in 1980, farmers complained angrily about violence on white-owned farms in the province of Matabeleland and denounced government plans to force some white farmers to sell their land for the resettlement of black peasants.

The situation in Matabeleland, where 16 farmers or members of their families have been killed this year by dissidents opposed to the government of Prime Minister Robert Mugabe, was the subject of two closed meetings with Emmerson Munangagwa, the minister responsible for security.

The killing of farmers by dissidents "has had a devastating effect not only on the morale of farmers but also on their confidence in the security forces to protect them," one landowner said.

More than half of the white-owned farmland in the province is reportedly up for sale because of the violence. It is believed that well over 1,000 black civilians have been killed as a result of Army retaliation against the dissidents. After today's meeting, Munangagwa conferred with Mugabe.

Many of the 5,000 white farmers, who produce the bulk of the food in the country, are concerned over the shift in government land-acquisition policy announced by Moven Mahachi, the minister of land, resettlement and rural development.

"Compulsory measures will be used to achieve consolidation of blocks of land in areas where some landowners refuse to offer their land for sale to government voluntarily," Mahachi said.

Until now, the 5 million acres bought by the government for resettlement of peasants has been acquired on the basis of "willing buyer, willing seller."

Mahachi criticized "the attitude of certain landowners who . . . persistently harass the officials in my ministry" over leasing of state land and said, therefore, that the process would stop.

He said the government's socialist policy sought to "convert the land ownership and tenure system from private ownership and uncontrolled land use permitting a high degree of exploitation of man by man, to either producer cooperatives or state farms." In addition, he said the remaining private holdings must be reduced in size but production must also be increased.

At the same time, Mahachi said he wished to "reassure farmers that the government has no intention of disrupting the success of the commercial sector of agriculture."

Responding to Mahachi's announcement, Sinclair said that the government was in effect, saying, " 'If you're not a willing seller, we'll make you one.'

"The feeling of insecurity felt by the commercial farmer engendered by rhetoric and statements that his tenure is in doubt, all has a debilitating effect."

He added, "Put a commercial farming operator with secure tenure against any other system and he will out-perform the other system all the time."