A U. N. special envoy warned Tuesday that southern Africa was plagued by widespread food shortages, poverty and AIDS deaths that were leaving behind millions of orphans and destabilizing societies.

"What is happening in southern Africa absolutely represents the most serious humanitarian crisis in the world today," the envoy, James T. Morris, said at a news conference here.

Morris visited Malawi, Mozambique, Swaziland and Namibia over the past week but reserved some of his strongest language to describe conditions in Zimbabwe, a deteriorating nation whose leaders declined to meet with him.

Nearly 5 million Zimbabweans are vulnerable to hunger in the year ahead, and life expectancy has fallen to 33 because of an HIV rate that is among the highest in the world, with one out of three non-elderly adults infected, Morris said.

"We were terribly disappointed not to be able to visit Zimbabwe," he said.

Zimbabwe's president, Robert Mugabe, has acknowledged that AIDS is a major problem in his country, telling a conference in the capital, Harare, last week that even members of his own family have contracted the disease, according to news service accounts.

Mugabe, who has presided over a chaotic campaign to seize farms owned by whites and redistribute the land to Zimbabwe's black majority, told Britain's Sky News last month that the nation no longer needed food aid. "We are not hungry. It should go to hungrier people, hungrier countries than ourselves," he said. "Why foist this food upon us? We don't want to be choked. We have enough."

Morris said last year's harvest would have to be doubled for Zimbabwe to feed its 12 million people. Mugabe's government has projected a near-tripling of the harvest, from 980,000 metric tons to about 2.8 million metric tons.

Morris said he knew of no evidence to back Mugabe's claims and that a crop estimate that was to have been done in conjunction with U.N. officials had been suspended by the Zimbabwean government.

Moving from serious shortages to surplus in a single year would be "unprecedented . . . anywhere in the world," Morris said.

He also said that the World Food Program would assist Zimbabwe if the government requested it, although procuring and delivering food can take weeks or months.

Conditions are bleak elsewhere on the continent, Morris added. There are 11 million AIDS orphans in sub-Saharan Africa, and the virus that causes AIDS is rapidly killing the most productive members of societies. Schools are losing teachers to the disease faster than new ones can be trained.

The toll has overwhelmed public health systems, and many trained health workers are migrating to find better paying jobs. In Malawi, for example, only 100 nurses out of 480 trained in one recent class are working there as nurses, Morris said.

One of the few bright spots in southern Africa is Zambia, which has overcome food shortages and now has a surplus of about 200,000 metric tons. It is among the nations that welcomed white commercial farmers who fled neighboring Zimbabwe during land-reform efforts in recent years.