Mozambique, one of the world's poorest lands as part of the Portuguese empire for centuries, has become even poorer in its eight years of independence.

Plagued by two decades of war, it is still trying to return to the economic levels of 1975 when Lisbon gave up control after a 10-year guerrilla war.

All but about 15 percent of the 200,000 Portuguese settlers fled. With their departure went the vast majority of trained manpower, most of the literate population and much of the equipment that could be moved. What could not be moved was often destroyed.

Every indicator of growth listed by the World Bank is negative for Mozambique for the period 1970-1980.

The U.S. Embassy estimates the per capita gross national product of Mozambique's 12 million population, living in a country twice the size of California, is $140--about one-hundredth that of the United States.

Contact with Portugal dates back five centuries, since the epic exploration of the Indian Ocean by Portuguese navigator Vasco da Gama in 1497-99, but in Europe's 19th century "scramble for Africa" Portugal's "right" to Mozambique was not recognized until the Congress of Berlin divided up the continent in 1885. Firm control from Lisbon was not established until the early years of this century.

With Portugal itself a backward country, Mozambique achieved little development but mainly served as a source of raw materials and an outlet for excess Portuguese manpower.

A western diplomat, referring to the transfer of resources from rich to poor nations, known in economic parlance as North-South, jokingly described Portuguese aid to Mozambique as "South-South."

Although it has vast coal reserves and potential water power, Mozambique's chief asset is its location. Its three ports of Maputo, Beira and Nacala along the 1,300-mile Indian Ocean coastline and the railways connecting them to landlocked countries in the interior are vital to black African development.

The nine-nation Southern African Development Coordination Conference (SADCC) regards the Mozambican transportation system as the linchpin for black African economic independence from South Africa, which now controls most of the trade of these countries.

For Zimbabwe, Zambia, Malawi, Botswana and Swaziland, Mozambique's ports are the only access to the sea other than through South Africa. The SADCC, which also includes Angola, Tanzania and Lesotho, is seeking $500 million in western assistance over 20 years to improve the ports to reduce dependence on South Africa.

In addition, Zimbabwe's main lifeline for petroleum is a pipeline from Beira to Mutare, on the border with Mozambique.

Mozambique's hidden war against the Mozambique National Resistance, however, has played havoc with the country's ability to take advantage of its transportation potential.

The MNR has blown up sections of the pipeline and kidnaped expatriate technicians at a pumping station. Saboteurs coming in from the sea and believed to be South African destroyed most of Beira's oil-storage facilities in December, causing acute fuel shortages in Zimbabwe for two months. Buoys at the port have also been destroyed, delaying shipping.

The road and railway bridges across the Pungwe River outside Beira were blown up in 1981, stopping cross-river transportation for six weeks. Numerous trains have been attacked, with more than 100 killed in the two worst incidents, and the Beira railway line has suffered more than 50 explosions in the past three years, according to Ramiro Silva, director of railroads for central Mozambique.

Three years after Zimbabwe's independence, most of its trade still goes through South African ports although shipping costs are four times higher than in Beira, which is much closer to Zimbabwe. Last year Beira handled just 1.6 million tons of freight from neighboring countries, only half the amount before Mozambique's independence in 1975.

At the same time, Mozambique and South Africa continue to trade despite the war. One foreign shipping agent, who declined to be identified, estimated that in a busy month 60 percent of the exports shipped through Maputo are from South Africa. Maputo is closer to South Africa's mines than many South African ports.

Maputo is also a convenient port for countries wanting to do business with South Africa secretly to avoid political embarrassment.

When Kenya had a corn shortage three years ago, South African corn was sent from Port Elizabeth to Maputo and then shipped to Mombasa, Kenya, with a laundered Mozambican invoice even though Mozambique is a chronic grain importer.

Still, a western diplomat estimated that the country is losing more than 50 percent of its potential income from transport. Some of the loss of trade is undoubtedly connected with deterioration of facilities because of the post-independence exodus of Portuguese technicians. The ports are being upgraded, but full trade potential cannot be realized without an end to the war.

So far, a western diplomat said, the war has "smashed the dream of Mozambique as a transport route for the SADCC. The cost for South Africa is cheap"--just supplying the MNR with weapons, ammunition, training and logistical support, the envoy said.