THE JOB of the secretary of interior boils down to a balancing of fiercely conflicting claims on publicly owned resources. The secretary has to reconcile his duty to preserve the country's remaining wilderness with the needs for recreation and land of a growing population. As protector of wildlife and endangered speicies, he also oversees an invaluable genetic reserve, but on whose preservation often conflicts with immediate human needs. He is in charge of biological resources -- from the grazing lands of the West to the valuable fisheries of the coasts -- where immediate production and long-range productivity dictate different handling. Above all, he must manage the vast federally owned lands, trading off the country's pressing interest in energy and mineral resource development with all of these, and more.

Never have the resources in Interior's jurisdiction been under greater pressure than they are now. Western coal mining is beginning a period of explosive growth. Oil shale and other synthetic fuel projects are leaving the drawing boards. Everywhere in the West the water supply is dwindling, threatening agriculture, ranching, energy development and even everyday living. More and more Americans are flocking to overburdened national parks and wilderness areas. More and more plant and animal species are threatened with extinction. In short, there are few if any appointments Mr. Reagan will make where the official's ability to make sound and balanced judgments will be felt for so long after he is gone.

Mr. Reagan's appointee will also have a long and honorable tradition to answer to: Republicans from all ideological corners of the party have been shapers of farsighted interior policy for more than 100 years. Yellowstone National Park, the country's first was created by Republican President Ulysses S. Grant. Theodore Roosevelt's proudest achievement was the vast acreage he added to the system. Gifford Pinchot, the father of modern forestry, was the first to recognize that development and preservation could and should coexist on public lands. More recently, Republicans like Russel Train, Walter Hickel, William Ruckelshaus and Rogers C. B. Morton have added to the record of prudent management.

Ther president-elect has said that he is looking for someone to balance "environmental extremists," but in naming James G. Watt he appears to have gone to an opposite extreme and chosen someone who has demonstrated little understanding of the Interior secretary's role as trustee, on behalf of the public, of the bulk of the nation's natural resources. In remarks at yesterday's press conference, Mr. Watt professed to be keenly concerned with balancing the claims on the department in a judicious way. But his background proclaims him to be an undiscriminating advocate of private development interests and a man with a overriding bias in favor of immediate exploitation of resources rather than long-range management.

Sound policy grows in part from the tension between competing views. In any administration, regardless of its philosophical bent, Interior should be speaking on behalf of concerns different from, for example, those of the departments of energy, commmerc and agriculture. Judging from the available record, it does not seem likely that it will do so under Mr. Watt's guidance.