U.N. officials coordinating the global relief effort for famine victims in Africa estimated this week that an additional $1.6 billion will be needed this year beyond the known $2 billion in pledges and contributions. An official said that since there has been no sign of slackening in international aid, he was optimistic about getting the added funds.

The U.N. team, headed by F. Bradford Morse, an American who also runs the U.N. Development Program, will hold an international conference in Geneva on March 11 to generate new pledges and coordinate aid with donor countries, recipients, private agencies and international organizations. Vice President Bush is to represent the United States at the meeting.

"Any shortfall in the response," Morse warned in a 92-page report listing specific needs in the 20 African nations affected by the famine, "must be measured not just in terms of a deficit in funds available but in terms of human lives lost unnecessarily." The report said the additional funds are needed to sustain the 30 million people "seriously at risk."

Some Western European diplomats, however, have been critical of the U.N. team's delay in compiling and issuing the aid statistics. One ambassador said, "They should have been out two months ago when they were needed."

A U.N. official working in Morse's Office for Emergency Operations in Africa, which was set up last December, said there is no sign that the aid flow from governments and private citizens is starting to slow. Relief officials in Africa frequently have expressed fears that last fall's television-prompted outpouring of concern for famine victims would fade just as food needs increased this spring and summer.

"Many face deficit problems at home, but governments have sustained their contribution levels," the official said. "And the public, too, is aware and contributing. We have no indication that the $1.6 billion will not be there by the time it is needed over the course of this year." The $1.6 billion would be in addition to the slightly over $2 billion already pledged or contributed.

He said that the estimated total need could fluctuate either way for any one of several reasons -- "It may rain somewhere we don't expect it too, or the dollar could collapse."

Beyond the need for coordination -- sending the right supplies to the right place at the right time -- the United Nations foresees major logistical bottlenecks this spring in the port and road facilities serving Mali, Chad, Ethiopia and Sudan in the east. "We need the equivalent of five more functioning ports to bring in the monthly flow we will require," a U.N. planner said.

He listed other problems hampering the relief effort, such as worms eating the early crops in northern Kenya; floods in Mozambique that are washing away food crops, and expected spring rains in Sudan, which would prevent delivery of supplies to outlying areas by road and could make it impossible for helicopters to land.

The report warned that despite some improvement in parts of western and southern Africa, the overall crisis "shows little sign of abating in the near future even if drought conditions were to improve markedly during the next rainy season."

Of the 30 million people at risk -- a fifth of the total population of the 20 countries -- about 10 million have had to abandon their lands in search of food, water and pasture. Even if there are crops this year, it will not be until fall that they begin to ease the immediate food needs in the areas hardest hit.

"If the rains come, it will not be until November that we can begin to estimate the needs for 1986," said the U.N. planner.

For Ethiopia, the country hit hardest by the drought and famine, the report estimates that $760 million worth of aid has been given or pledged, but the "unmet needs" for 1985 are $380 million.

The estimate of people "at risk" in Ethiopia has risen in the past month by 200,000 to 7.9 million, and the total is expected to grow well above 8 million before the next harvest. After April, grain needs will increase to 125,000 tons a month, requiring an increase in port capacity (which is already being prepared) and "very close scheduling of food aid shipments." In addition, massive air drops will be needed in inaccessible regions.

The report made no reference to charges that Ethiopia has been preventing shipments to rebel-held areas, except to say that "in some countries, internal transport problems are compounded by internal security questions."

The other eight countries listed as having vast life-threatening problems were:

Angola, with 500,000 people at risk, pledges of $30 million and a need for $33.7 million more for 1985; Burkina Faso (formerly Upper Volta), 500,000 at risk, pledges of $26 million and a gap of $68.2 million; Chad, 1.5 million at risk, pledges of $64.5 million and a gap of $225.4 million; Mali, 1.2 million at risk, pledges of $47 million and a gap of $159.5 million; Mauritania, 1.1 million at risk, pledges of $35 million and a gap of $41 million; Mozambique, 2.5 million at risk, pledges of $135 million and a gap of $81.1 million; Niger, 2.5 million at risk, pledges of $60 million and a gap of $149.7 million; Sudan, 4.5 million at risk, pledges of $300 million and a gap of $191.3 million.

The other 11 countries, with lesser numbers of people at risk and, for the most part, smaller shortfalls in aid requirements, are Botswana, Burundi, Cape Verde, Kenya, Lesotho, Rwanda, Senegal, Somalia, Tanzania, Zambia and Zimbabwe.