Johannesburg — A Soviet shipment of ferrosilicon arrived at the docks of New Orleans this fall, typifying a trend that has the Reagan administration worried. The trend: The United States is increasingly reliant on imported minerals. And a number of these minerals are vital to the nation's defense and economy.
Ferrosilicon is not considered a ''strategic'' material. But processing silicon has been a bright spot in the US minerals sector. An ''invasion'' of that market, which industry insiders believe the Soviets are attempting for the first time, would further weaken the US minerals position.
To cope with the overall problem, the Reagan administration is considering subsidizing domestic production of certain minerals - something not done, with one minor exception, since the Korean war. The administration is requesting $200 million from Congress for the program in the 1984 fiscal year.
Top priority in the program would be a demonstration project for producing domestic cobalt, with an eye toward possible future subsidization. Funds would be allocated under the Defense Production Act, which comes up for renewal in Congress early in 1984.
But even if the subsidization program goes ahead, minerals experts are in agreement that US reliance on foreign minerals will not be quickly or sharply reduced. Indeed, in the short term, minerals dependence is more likely to rise as a result of the country's economic recovery and President Reagan's arms buildup.
Experts differ on whether US minerals dependence should be cause for alarm. Some see the US locked in a ''resource war'' that will ultimately lead to the equivalent of an oil crisis - with the US at the mercy of unstable and unfriendly minerals suppliers. Others believe US minerals reliance is manageable.
The Congressional Budget Office (CBO) in a recent report noted that dependence on imported minerals ''creates risks for the US economy and for national preparedness in the event of war.'' But it added there are ''significant benefits as well.''
The main benefit is that often minerals are imported because they are cheaper and that keeps down the prices of the end products that utilize minerals.
The extent of the problem as outlined by the CBO:
* The US is a net importer of 64 ''strategic and critical'' minerals and metals.
* US dependence on imported minerals is growing because of higher domestic demand and a less competitive US minerals industry.
* For some of the most critical minerals, the US relies on only a few countries, and some of these countries are regarded as potentially unstable.
* America's insurance policy against a wartime interruption of minerals - the national defense stockpile - is under-stocked. The reserve contains some 93 commodities, 80 of which are of mineral origin. Minerals stored range from diamonds to jewel bearings and are stock-piled as ore, as processed metal, or as an alloy with other metals. It will cost $11 billion to fully stock this minerals stockpile.
* There is no mechanism for dealing with supply disruptions that fall short of a wartime situation.
Growing minerals dependence is a byproduct of a modernizing economy in the postwar period. Generally, the US is requiring growing amounts of specialty steels and other alloys for high-technology products and military hardware.
Modern missiles use platinum in electrical contacts, and most platinum is imported from South Africa and to a lesser extent from the Soviet Union. Cobalt from Zaire and Zambia is essential for computers. The space shuttle uses more than 20 critical minerals, many of them imported. The Air Force's new B-1 bomber is made largely of aluminum alloys, which require Jamaican bauxite and Australian alumina.
Over the past 20 years, says the CBO, the US has grown increasingly reliant on imported titanium, tungsten, cadmium, zinc, cobalt, alumina, and bauxite. More dramatic, the US is now a net importer of items it used to export, such as copper and vanadium.
More recently, the processing of raw minerals is shifting overseas. The last American furnace producing ferrochrome shut down earlier this year, and there is only one furnace making ferromanganese.
The minerals about which there is most concern are cobalt, manganese, platinum group metals, and chromium. They are all considered ''strategic'' - meaning they are not easily replaceable and they are essential to the nation's economy or defense - and in all cases imports account for 85 percent or more of US supplies.
Further, the greatest known reserves of these metals are in southern Africa, a region of political and economic turmoil.
Hans H. Landsberg, a minerals expert at Resources for the Future in Washington, generally holds the view that US minerals dependence is ''manageable.'' But he agrees a potential threat looms in Africa.
South Africa is a leading minerals supplier to the US. But a too-friendly US stance toward Pretoria's white regime could alienate the region's black supplier states, Zimbabwe, Zaire, and Zambia. Or it could alienate any future black government in South Africa.
The other worrisome scenario pointed out by the CBO: What if racial conflict in South Africa escalates to the point where the West is pressured to impose economic sanctions?
The main tools for coping with minerals dependence:
* Stockpiling of certain minerals. The federal government has been stockpiling since the 1950s. The present goal of the national defense stockpile is enough stocks to wage a three-year war.
Experts suggest several steps to improve the stockpile. One is simply to lower its objective to being able to meet the needs of a one-year war. Some also recommend stricter guidelines on how stockpiled materials are to be used. Although the stockpile is designed for military emergencies, Mr. Landsberg says sales from the reserves have been used in the past to reduce the federal budget and to keep producer prices low.
The CBO suggests the US should start with a comprehensive audit of the stock-pile. As it is now, the General Services Administration, which manages the stockpile, lacks funds to survey in detail more than only a ''very few'' materials each year, says the CBO.
Landsberg endorses the use of stockpiles for more than just military emergencies. He suggests the private sector buy and maintain some of the stocks for use in routine supply disruptions. Sweden, Switzerland, and Japan maintain ''economic'' stockpiles.
* Substituting some minerals for others. The replacement of accessible minerals for less accessible ones happens automatically when existing supplies become erratic or too costly. For instance, political shocks that threatened cobalt supplies from Zaire in the 1970s led to a move away from cobalt in the fabrication of magnets and to less use of cobalt in alloys for critical engine parts.
Boron, produced largely in the United States, has been used successfully in place of imported chromium for some steel products.
To be better prepared for supply disruptions, some experts say the US should spend more on substitution research and development. ''What is needed,'' Lands-berg says, ''is a stockpile not only of materials but of materials technology.''
The CBO suggests the US needs to conduct more research in the area of nonfuel minerals.
* Encouraging new supplies of minerals. This can be done by opening up more federal lands for exploration, subsidizing production, or encouraging through tax laws foreign investment in new areas not considered unstable or unreliable.