The foothills of the awesome Himalayas are slowly but inexorably being washed away in a process that could ultimately transform this beautiful land into a mountainous desert.

Unchecked deforestation and the resultant soil erosion already have denuded vast areas of the mountain kingdom of Nepal, not only causing irreversible ecological damage there, but also threatening the course of rivers and the vegetation upon which nearly 1 billion people in the South Asian Subcontinent depend for survival.

Twenty years ago, nearly 60 percent of Nepal's land mass was blanketed by thick forests. But that figure has dwindled to 19 percent, according to State Planning Commission estimates, and it continues to decline despite recent acceleration of forestry schemes and other efforts to curtail the felling of trees.

If the degradation is not reversed, Nepalese environmentalists say, the hills that cover more than half the country will be grotesque sunbaked pyramids by the end of this century, and the wasteland will not be reclaimable.

"Now, tourists come here because of Nepal's unsurpassed beauty," said Karna Sakya, secretary general of the Nepal Nature Society and head of the Nepal Heritage Society. "In 20 years, they will be drawn here to see what extraordinary ruin man has done to nature."

Concern over deforestation is not new in Nepal, but now there is a heightened sense of urgency that has prompted environmentalists to propose increasingly drastic remedies to save the mountain forests.

The most controversial of these is a draconian measure advanced by Sakya and other Nepalese ecologists to resettle forcibly more than 900,000 mountain dwellers from the hillsides of northern Nepal to the fertile lowlands in the Terai region in the south.

Reflecting the new level of alarm in a growing segment of the environmental community, Sakya said, "We have to follow certain doctrinaire policies, and we have to be content with dogmatic adherents. There is no time left for a cautious approach."

Under the resettlement scheme, which is opposed by government environmentalists, all those who live above the 30-degree slope line in the highlands--about 7 percent of Nepal's population--would be declared to be living on nationalized land and then moved 100 miles to the south, where intensive agriculture development programs would be offered.

Increasing numbers of mountain dwellers have been migrating to the Terai anyway, Sakya noted, and the scheme would merely institutionalize the phenomenon and make it policy.

The proposal, Sakya said, was born out of a worsening of the vicious circle of socio-economic and ecological causes and effects that has plagued Nepal for years.

Chief among the problems is wood--the poor man's fuel--which provides 85 percent of the country's heat and cooking energy. On the average, a Nepalese family consumes 1 1/2 tons of fuel wood a year.

With the population at 14 million and growing at 2.4 percent annually, and the per capita income at only $120 a year, the demand for fuel wood is constantly increasing as the supply shrinks.

Moreover, environmentalists say, increasing numbers of mountain dwellers are living as squatters on forested land and cutting trees to grow corn and potatoes on terraced plots that have neither retaining walls nor adequate drainage.

When the monsoon rains come from June to October, the topsoil is washed away and massive landslides occur, uprooting more trees and sometimes laying waste to half a hillside. The mountain dwellers move on to squat elsewhere, and the process is repeated, Sakya said.

Compounding the problem is a constantly growing livestock population in the hills; about 75 percent of the fodder for Nepal's 10 million grazing cattle comes from the forest, according to the environmentalists.

"Mountain people have very little knowledge about ecological balance," Sakya said. "All they know is that they are hungry and need to find food and fuel. So they squat wherever they want."

Sakya was Nepal's first wildlife officer, but he resigned from the government in 1972.

The deforestation damage goes far beyond Nepal's borders. Mountain topsoil is washed down in rivulets to the rivers, where it is carried through India and Bangladesh as far as the Bay of Bengal.

Apart from raising the beds of Nepalese rivers an average of 13 inches annually, the silting is altering the flow of water throughout the Subcontinent. Over the years it has created whole new islands in the Bay of Bengal and caused navigational hazards at the port of Calcutta on the Hooghly River.

The Indian government long has been alarmed about the effects of Himalayan erosion on its waterways, but at the same time has imported 75 percent of the timber harvested in Nepal, including most of the trees felled in the Terai region. The Terai, which once was densely forested, has been largely denuded, and forest officials estimate that in 15 years it will have no commercial forests.

The Nepal Heritage Society estimates that the Terai currently has about 1 million acres of unprotected land that can be used for planting food grains, with a potential capacity of producing 3,400 pounds of rice and 440 pounds of lentils per acre each year.

Under the resettlement scheme, the Himalayan mountain people would be resettled in these areas and given assistance in intensive farming to increase Nepal's annual food grain production growth rate, now 7.5 percent.

Government conservation planners argue that apart from the enormous social dislocation that such an extreme step would cause--not to mention the logistical complications and huge costs--resettlement of the mountain dwellers would merely shift the ecological problem from one area that is being damaged to another that is trying to recover from environmental degradation.

Officials pointed out that some mountain people already are migrating to the Terai in search of better cropland, and they said that the government's efforts would be better directed toward expanding forestation projects and discouraging indiscriminate felling of trees. The government also should concentrate on providing alternative fuel resources and introducing forestry courses in schools to give the hill people a sense of environmental responsibility, they said.

"Community forests" established by the government are beginning to provide wood fuel for the hill people and also are reviving the bond between villagers and their forests that once maintained an ecological balance in the Himalayas, state forestry officials said.

Aided by the Agency for International Development and other organizations, Nepal has numerous forest conservation projects under way, including schemes to develop more fuel-efficient stoves and alternative energy sources, experiments in growing fodder crops to provide ground cover, reforestation and the establishment of an institute of forestry management.

However, as one western diplomat who has monitored Nepal's environmental efforts said, "Progress is heartbreakingly slow and the problem is almost as big as man and nature combined."

In the meantime, Nepal's most precious commodity--the spectacular Himalayan beauty that annually lures nearly 40,000 trekkers and tourists who are the country's largest source of foreign exchange--is being eroded by man and nature.

"We've been talking and talking, and the mountains are still being washed into the sea," said Sakya. "It's time to do more before it's too late."