Though rains have come to Africa, serious problems remain. Crop harvests threatened by pests and millions of people still homeless

Twenty-one million people -- at least -- still hungry. Two and a half million people still forced to live away from their homes and farms -- at least.

A ``grave'' threat to precious grain now ripening in the Sahel after the best rains in four years: clouds of voracious grasshoppers and grain-eating birds called quelea.

Little has yet been done about either pest, officials say. Action is urgently required.

These three points about hungry Africa emerge from talks with United Nations officials, and from new UN documents, here and in Rome.

Officials are extremely concerned that many people in North America, Western Europe, Japan, and Australasia think the worst African drought of the century is now yesterday's news.

Yes, they say, the drought picture is generally improving, but six dark spots remain for 1986: Ethiopia, Sudan, Angola, Mozambique, Botswana, Lesotho. In these six alone, some 21.4 million people are still suffering because rains have been scattered, light, or just haven't come.

In the same six, upwards of 2.4 million have been displaced from their own tribal areas, according to the Office for Emergency Operations in Africa (OEOA) here.

UN relief officials make two more points: six is a great improvement on the crisis-list of 20 nations monitored all this year by the UN Food and Agriculture Organization (FAO) in Rome. But the six (and others) will need urgent help next year, underscoring that the famine emergency, in the UN view, cannot be forgotten or ignored.

Late information from reports received by OEOA and by the UN World Food Program (WFP) based in Rome:

Ethiopia: Government officials say that between December 1984 and August 1985, 625,000 tons of grain have been distributed to 6.2 million people each month.

The officials say 214,000 people have been displaced (the UN estimates 337,000). Some 183,000 families have been resettled from north to south, the government says, adding that its resettlement target is 300,000 families.

As for 1986, 5.8 million people could be affected in 13 major regions. The OEOA reports a preliminary estimate that 1.16 million tons of food aid may be needed by the 5.8 million people. United States aid officials in Washington have so far put the figure somewhat lower.

The US Agency for International Development is giving at least $2.4 million to start up the largest truck fleet ever provided to an African country to haul grain.

Sudan: Bumper crop of sorghum expected, but as WFP officials say, ``There's nowhere to store it.'' Appeal is going out for 27 million bags.

Truck and auto fuel is starting to run short. WFP has just provided 3,400 tons of fuel, making a total of 7,000 tons this year. The fuel is urgently needed for 150 trucks already operating under WFP and for 200 more expected before the end of the year from Italy, Band Aid, The Netherlands, World Vision, and the Organization of Petroleum Exporting Countries.

In the remote western area of Darfur, crop prospects are not as good as hoped, according to OEOA, because of seed shortages and uneven rains.

Lesotho: National emergency declared Oct 10: no proper rain for the last five years. More than half the population of 1.4 million are affected by the famine, UN officials in New York report.

China and North Korea have each donated 1,000 tons of corn. Much more will be needed.

Botswana: Of a population of 1.1 million, 610,000 are said to be affected by drought. Botswana urgently needs 11,706 tons of grain before June, $2.1 million for health care, $1.7 million for water supplies and sanitation, $5.9 million for fertilizer and other food-growing needs, and $6.4 million for ``relief and survival needs.''

The Sahel: In Mali, local reports speak ominously of 40 to 60 grasshoppers infesting each square yard of land in some areas of Mali. ``No response'' has yet come from donors to meet the challenge despite pleas by the Mali government, the UN reports, although FAO provided emergency aid of $238,000 in September.

In the Niger delta of Mali, the UN Development Program has provided $31,000 to try to control the quelea birds after ``substantial nesting activities'' were reported.