Third World nations must plant trees to cover an area twice the size of Texas by the year 2000 to stem environmental degradation and maintain living standards, a research organization said Saturday.

The Worldwatch Institute said replacement trees are needed to meet demands for fuel and industrial wood products and to stem erosion, to return nutrients to the soil and to protect water supplies.Another compelling reason is that planting more trees would help stabilize the climate by slowing buildup of carbon dioxide in Earth's atmosphere and mitigating the trend toward global warming, the so-called greenhouse effect.

"It gives us more reason to be putting financial resources there," researcher Sandra Postel said.

Postel and her colleague Lori Heise estimated that trees must be planted on 130 million hectares, equal to about 320 million acres, an area slightly larger than Ethiopia and twice the size of Texas.

Forest cover in industrial countries is relatively stable. But worldwide each year, an area of trees the size of Connecticut 40 million acres or 16 million hectares is gathered for fuel wood, harvested for commercial timber or cleared for crops or cattle ranching.

Just as carbon-based fossil fuels such as coal and oil release carbon dioxide into the atmosphere, trees release carbon dioxide when they burn and decay.

Deforestation may add a fifth as much carbon dioxide to the atmosphere each year as combustion of fossil fuels. But growing trees counteract that trend by absorbing carbon dioxide through photosynthesis. Thus, more trees would help slow the global warming process.

"Expanding tree cover to satisfy demands for fuel and industrial wood and to protect soil and water resources could reduce net carbon releases from tropical lands by 47 percent," Postel and Heise said.

They said cutting deforestation rates in half in four countries with the most intensive forest losses Brazil, Indonesia, Colombia and Ivory Coast would cut total net releases of carbon by 23 percent.

Other arguments deal with more tangible benefits. Postel and Heise said that unless tree planting is accelerated, half the people in the developing world will lack a sustainable supply of fuel wood by the year 2000.

In rural parts of the Himalayas and Africa, women and children spend between 100 and 300 days a year gathering fuel wood. That takes them away from farming, education and other productive activities.