POOR COUNTRIES sometimes think of environmental protection as a luxury for the rich. But violation of the basic conservation rules threatens the whole process of development. Where people are hungry, overuse of the land is a pressing temptation. More than half of India's soil currently shows signs of degradation. In wide areas, flooding and erosion wash nutrients out of the earth faster than farmers can replace them with fertilizer.

The United Nations Environmental Program, in alliance with several other conservation organizations, is undertaking a campaign to raise the consciousness of governments. It invites them to pay closer attention to the destructive side of conventional development. It emphasizes the continuous losses of that most limited of natural resources, the world's supply of productive farm land.

The supply of arable land is diminished when new housing or roads are built in Virginia. It is also diminished when grazing land in central Africa is overstocked and, with the stripping of the cover, the Sahara edges southward into it. Agronomists and soil engineers know a great deal about the costs of careless development. The purpose of the U.N. Environmental Program and its allies, in the document that it calls a world conservation strategy, is to press this knowledge on the people who actually make decisions, public and private, about investment and land-use policy. Like all statements of consensus, this one has its defects. It neglects, for example, the sensitive subject of population growth.

But it delivers a message of some urgency, and delivers in it terms calculated to win a hearing in very diverse places. It provides a series of standards against which any government's decisions can be measured. Above all, it offers a warning that the long struggle to protect land and water is not being won. If the present rates of degradation persist, it says, close to one-third of the world's arable land will be destroyed by the end of the century.