Backed by the artillery of the conservative right, the Reagan administration has begun a campaign to end U.S. dependence on foreign supplies of a small group of strategic metals and minerals that are vital elements in the nation's industrial capacity.

On Friday, President Reagan announced a government plan to purchase $100 million in strategic minerals to build up defense stockpiles, calling it the first step in a program to "decrease this nation's vulnerability."

Reagan administration officials led by Interior Secretary James Watt are determined to open wilderness areas and other federal lands to exploration and production of minerals. The minerals issue dictates new policies toward the mineral-rich countries of southern Africa and a helping hand for the U.S. mining industry.

And it caused the abrupt dismissal March 8 of the entire U.S. delegation to the United Nations Law of the Sea conference because the Reagan administration feared the conference treaty could jeopardize deep-sea mining of minerals by U.S. firms.

Expectations of a complete change in policy are taking hold. The prospect of a minerals boom has led three of the nation's giant oil companies to invest billions in nonfuel mineral resources. Many former "gold bugs" now are touting manganese, titanium and molybdenum. One of Wall Street's biggest firms, Bache Halsey Stuart Shields Inc., this month began selling exotic metals to investors -- evidence of a new, speculative fancy.

A rear guard of environmentalists and some resource experts say the fears of critical mineral shortages are exaggerated. "We are dependent, but we aren't vulnerable if we have ways of getting these minerals from somewhere else and stockpiling them," says Hans Landsberg, a minerals expert at Resources for the Future, a Washington research organization. Stable countries such as Austrailia, Canada, Mexico, Brazil and Venezuela, are important exporters of many strategic minerals, he noted.

One potential exception is cobalt. In their view of a troubled world, key Reagan administration officials see the prime sources of vital minerals like this in hostile or vulnerable hands.

"The United States is now dependent on foreign sources for 100 percent of our manganese and 100 percent of our cobalt," Watt said recently, citing two key components of the high-quality steel used in jet engines, artillery, shells and armor plate.

And the chief sources of these metals currently include the Soviet Union and the nations of southern Africa that watch each other suspiciously from across a color barrier -- South Africa, Zaire, Zimbabwe and Tanzania.

Supplies of cobalt could be cut off, either by an effective United Nations boycott of South Africa, or conflict between white South Africa and its black neighbors, experts note.

According to Secretary of State Alexander Haig, the efforts by the Soviet Union to extend its influence in Africa are the beginning rounds of a "resource war" aimed at the United States and its industrial allies. He made that assessment last September in testimony before the House Mines and Mining subcommittee, as president of United Technologies Corp., the nation's third largest defense contractor and a major user of cobalt.

The nation's current cobalt stockpile -- 40.8 million pounds -- is only half the necessary amount, and a cutoff of that mineral would reduce United Technology's output by 25 percent within a year, Haig said.

The stockpiling program announced Friday wil begin with the purchase of 1.2 million pounds of cobalt at about $25 per pound.

Other materials that are being considered for the stockpiling programs are manganese, bauxite and aluminum oxide, platinum metals, vanadium and nickel. The United States currently imports more than 75 percent of its requirement of each of these materials.

Stockpile purchases will be financed by sales of surplus supplies of other government-held materials, including silver and tin.

But Watt says he is not content with that. He has taken on the responsibility to "foster and encourage" the U.S. minerals industry. In recent congressional testimony, he said he sees himself as a "friend" of the industry, "not as a representative of private mining interests, per se, but as a spokesman for the very real public interest involved in the protection and preservation of a strong minerals section."

Watt said he is considering a new policy "permitting exploration for and development of minerals within the wilderness system. I will oppose single-use designations of those lands if that means a significant loss of fuel or nonfuel mineral resources," he said in Senate testimony March 2.

"The best answer to minerals availability is domestic production," said Watt -- not stockpiling.

That is the core of the debate Landsberg says that with careful attention, an adequate minerals stockpile capable of lasting six months to a year can be built up, permitting the country to continue meeting industrial needs from foreign sources.

He discounts the worries about a possible mineral cartel forming to limit supplies and raise prices as the oil exporting nations have done since 1973. The stable mineral exporting countries wouldn't do that, and the vulnerable African countries are "living hand-to-mouth" and can't do without the income from mineral exports, he said.

The prospects for extensive domestic production "are not very good," he adds. "We have done it before," he said, "and every time we try to push domestic production, the costs are very high. The question is, do you want to load up the American economy with costly minerals if you can get them from somewhere else, for less."

Not surprisingly, Watt's strategy alarms environmentalists.

"It's a myth that public lands aren't open to mineral exploration," says Brock Evans, associate executive director of the Sierra Cluab. "Only 80 million of 760 million acres of public lands are totally closed -- primarily national parks, defense department reservations and lands set aside for particular uses, such as oil shale mining or reservoirs."

"The bulk of the lands that are completely closed are in Alaska," he said. Even there, seven sites identified by the Stanford Research institute as "world class" mineral deposits were left open for mining. "Not one of those sites is being mined, simply because its cheaper to import than to mine in Alaska."

Environmentalists don't object to tapping public lands "when the national security is truly at stake and not just the profits of the mining companies," said Evans. Boundries of the River of No Return Wilderness in Idaho were redrawn at the urging of mining interests to exclude a potential cobalt mine, he notes. Owners of the mine recently announced they had decided not to open the mine because it was cheaper to import cobalt from Africa.

The debate is "fundamentally ideological," claims Evans. "The mining people are far more rabid than anybody else about the issue of public lands. They just can't stand to see land sitting there not being used. They'll use any argument" to justify opening up public lands.

The strategic minerals lobby is led by the American Mining Congress and backed by the American Iron & Steel Institute, the U.S. chamber of Commerce, the National Association of Manufacturers and dozens of Fortune 500 companies in the mining, metals and manufacturing businesses. The most vocal private spokesmen include Allegheny Ludlum, a major supplier of alloying metals, and United Technologies, Haig's old employer.

With their powerful backing, the House mines and mining subcommittee, chaired by Rep. James Santini (D-Nev.), has put together a package of financial and tax incentives that Santini says are vital to the nation's mineral independence.

At the top of the list is maintaining the percentage depletion allowance that permits mining companies to avoid paying income taxes on much of their profits and continuing to let miners deduct all their exploration and development costs; both provisions have come under attack from tax reformers in Congress.

The use of investment tax credits to encourage spending on mineral development should be expanded so all investments in mining facilities are eligible for the credit, the Santini subcommittee recommended. If mining companies don't have enough taxable profits to utilize the tax credit, they should receive an equivalent amount in cash.

The mining panel also urged special accelerated depreciation for investment in mineral production; if they don't get such consideration, mines should at least benefit from the Reagan administration's proposed revision in tax write-off rules. Tax-exempt financing for environmental equipment at mines and other facilities also was recommended by Santini's subcommittee.

Strategic minerals advocates are expected to introduce legislation this year to provide tax incentives to businesses and investors that buy and stockpile metals.

Investment tax credits ought to be available for stockpiling, they argue, and owners ought to be able to claim depreciation on stored hoards of critical minerals. Depreciation is not allowed on stockpiles of other commodities, and critics contend it will be difficult to make a case for writing down the value of a product that is more likely to be increasing in value over time.

The mineral industry is promoting changes in federal anti-trust laws that will allow competing U.S. firms to cooperate on overseas ventures, a practice that now is illegal.

The industry has urged the Reagan administration not to let anti-trust considerations stand in the way of acquistion of major mineral firms by oil companies, arguing that the oil firms can supply cash needed for mineral exploration.

Last week Standard Oil Co. of Ohio agreed to pay $1.8 billion for Kennecott Corp., the nation's biggest copper company. The week before Standard Oil of California bid $3.9 billion for AMAX Inc., another minerals company, but AMAX rejected the offer. Three years ago Atlantic Richfield Corp. bought Anaconda Copper, second only to Kennecott in U.S. production.

Investors with a little less money to spend can buy strategic minerals from Bache, which this month for the first time began selling exotic metals to investors.

Buying a ton of titanium or a truckload of manganese is a high risk, speculative play, Bache cautions. There is little public trading in small lots of metals so cashing in the investment could be difficult.

The leading promoter of strategic minerals as an investment is James Sinclair & Co. of New York, which recently put chromium, cobalt, germanium and manganese on its list of "primary investments" and also suggested antimony, indium, rhodium and titanium.

Sinclair, once the most ardent promoters of buying gold, also is touting indirect investment in strategic materials by buying the stocks of companies like Cons Durham, North America's largest producer of antimony, or South African Manganese, the world's principal producer of that metal.

Ike many strategic materials advocates, Sinclair has long-standing ties to South Africa.

Santini last summer led his subcommittee on a junket through the three African mineral kingdoms and concluded that black-ruled Zimbabwe and Zaire were too unstable to be counted on for strategic minerals.

"American thus has a vital interest in the survival of South Africa as a western ally," he said, "past U.S. approaches and policies in dealing with South Africa have been manifestly self-defeating and unsuccessful."

Moral Majority leader Jerry Falwell took up the "resource war" theme in one of his radio evangelism lessons. "It is hardly coincidental that African nations that contain the greatest reserves of strategic minerals also abound in Russian East German and Cuban military personnel," the Falwell broadcast said. "We are in a war, whether guns are being fired or not. It is ideological war, economic war, spiritual war. We must be prepared to do what is necessary to win." CAPTION: Picture, "It is my intention to move aggressively to [implement] a truly national minerals policy," said Interior Secretary James Watt. Maps 1 and 2, no caption, By Hatley Mason -- The Washington Post