Zimbabwe announced today that it had received pledges of $2 billion in aid over the next three years at a week-long donor conference, a figure experts say could allow this new African nation to escape the international dole thereafter.

A Zimbabwean official said the world had backed up its frequently stated "best wishes" for the new nation with money.And he acknowledged that almost all of the funds will come from the West, a fact likely to keep this strategically situated southern African nation on its Western orientation despite Prime Minister Robert Mugabe's lip-service to Marxism.

Faced with massive reconstruction after the ravages of a seven-year independence war, Zimbabwe undoubtedly will feel constrained to keep its Western donors satisfied since most of the aid pledges must be renewed annually.

Many delegates from the 36 donor nations and international organizations made it clear that they regarded the success of the newly independent nation as a key to the hopes for a peaceful solution of racial problems in white minority-ruled South Africa.

Success of a democratic, multiracial Zimbabwe after years of black-white strife could have a positive effect on its neighbor to the south and possibly help avoid a conflict in which the Soviet Union could be expected to supply weapons to nationalist guerrillas.

Some delegates thought Zimbabwe would have a good chance to become self-sufficient with the benefit of this one-shot assistance, barring political or economic difficulties with South Africa.

"In many respects, this is a first-world country with a Third World problem," an aid official said in explaining why Zimbabwe has a good chance to get off the international aid list.

He referred to the modern sector in the country, one of black Africa's most advanced after 90 years of rule by the white minority, but said the gap between that and the rural area was "horrendous."

Bernard Chidzero, minister of economic planning and development and chairman of the conference, put the differential in graphic terms earlier in the week:

"Average income in the modern sector is more than 20 times that in the subsistence sector. The urban black per capita income is only 10 percent that of the whites, while that of the rural black population is only 1 percent."

Prime Minister Mugabe, in opening the conference Monday, appealed for $2 billion in new aid for a concerted three-year program concentrating on land resettlement and development, war rehabilitation and technical assistance. l

New funds pledged at the conference actually totalled about $1.45 billion, but previous commitments raised total aid to $2 billion. Aid specialists could not recall a case where any new independent nation had received such a major boost.

The World Bank was the largest donor with $459 million in soft-term loans. Britain was second with $282 million and the United States third with $225 million. Most of the American and British aid is in the form of grants.

The United States pledge of $225 million, pending congressional approval, over the next three years is a sharp increase over the $50 million given in the first year of independence. The commitment was the first major sign of Reagan administration support for a black-ruled nation in southern Africa, an area of potential black-white conflict.

Other major donors were the European Common Market, France, West Germany, Sweden, Canada and the African Development Bank.

More that $116 million came from oil-rich sources, including Kuwait, Saudi Arabia, an Arab development bank and the Organization of Petroleum Exporting Countries.

The only communist nations on the list were China and Yugoslavia, which gave major arms support to Mugabe's guerrillas during the independence war.

No Warsaw Pact country pledged any money and, contrary to earlier reports, the Soviet Union did not attend the conference. Mugabe has been cool toward the Soviets partly because they supported his guerrilla rival Joshua Nkomo, now a minor partner in the government.

Moscow and Salisbury only agreed on opening relations last month and a Soviet delegation is currently visiting Zimbabwe to iron out details.

Chidzero said it was understood that the Soviets might later agree to a separate aid package but he could not give an amount.

He noted the Soviet contention that aid is a Western problem and that underdevelopment in the Third World is a product of "imperialism."

Nevertheless, Zimbabwe sought to send a delegation to Moscow last month to help prepare for the conference. The Soviets refused to admit the group.

The week-long meeting was an outgrowth of the 1979 British-negotiated peace agreement that ended the war and 15 years of illegal independence for the colony of Rhodesia.

The agreement prohibited seizure of land, the key issue in the war since the 3 percent white minority owns most of the best agricultural property, but Britain and the United States made vague promises of mounting a multi-donor effort if a settlement was reached.