THE AMERICAN Geological Institute, claiming to represent more than 50,000 geologists, geophysicists and other earth scientists, sounded the alarm Thursday over another alleged source of American weakness. The issue this time was U.S. dependence on imports of metals and minerals essential to the defense industry and to the economy as a whole.

This much was not new. The country's growing dependence on such imports has been a source of concern -- though not yet as much constructive action -- for some time. But the geologists injected an entirely new note with their claim that "the U.S. is in a resource war, conducted by the Soviet Union, whose objective is to interrupt or deny this country access to strategic and critical materials." An undeniable headline-grabber, but is it true?

The number of critical minerals is variously defined. Some cite 10 that are essential to national defense. Others list 13 basic industrial raw materials. Still other sources refer to 32 minerals as essential to the economy. But whatever one considers to be on the list, a comparison of U.S. and Soviet self-sufficiency yields the same answer: the Soviet Union can produce all or nearly all of its own needs for almost all of them, while the United States must import more than half of its needs for most of them. This growing dependence is reflected in a balance of payments deficit for non-fuel minerals that more than quadrupled during the last decade.

Moreover, the countries from which U.S. imports come are often not reliable sources of supply. The Soviet Union itself, for example, is the largest supplier of titanium, a key material in weapons production. Another key element, cobalt, is largely supplied by Zaire, whose government's instability was highlighted by the uprising in 1978. Many fragile or unstable African nations, particularly the Republic of South Africa, are the major suppliers of minerals.

The growing U.S. reliance on imports and the longtime Soviet concern for ensuring its own independence in this area are matters of fact about which there is little room for debate. The implications of this differnce for national security are another matter. Suppliers dependent on exports for foreign exchange earnings are not as free or as likely to cut off supplies as they are often portrayed as being. The growing potential to reduce U.S. import needs by recycling and reusing minerals and through the substitution of sophisticated new plastics and alloys for scarce natural materials are also often ignored.

But the central question posed by the geologists is whether the Soviet Union has in fact adopted a conscious strategy to deny U.S. access to mineral imports. The statement issued Thursday to the three presidential candidates provides no specifics to support the allegation.

Nevertheless, U.S. mineral needs are a real problem. The lesson to be drawn is the importance of a continuing, vigorous effort to strengthen U.S. relations with Africa and to resolve southern Africa's racial dilemma. Domestically, more attention needs to be given to conservation and reuse -- not to excessive and expensive stockpiling of more than a few truly essential strategic materials.