President Carter, evoking protests from environmentalists, said yesterday that he will open 36 million acres of roadless areas in the national forests to timber cutting, mining and motorized recreation.

He will also recommend, however, that Congress set aside 15.4 million acres as wilderness. Another 10.6 million acres will be set aside for further study.

The announcement comes after eight years of controversy over how to allocate these 62 million roadless acres in the 187 million acres of federally owned national forest.

Carter's decision-which essentially reaffirms a Department of Agriculture recommendation in January-gave timber companies what they wanted in order to soften industry opposition to a reorganization, environmentalists charged yesterday.

Carter has proposed moving the Forest Service to the Interior Department-a reorganization that is fiercely opposed by timber companies.

The White House is selling the store for a mess of pottage," said John McComb of the Sierra Club. "Reorganiztion is probably dead anyway."

However, Rupert Cutler, assistant secretary of agriculture, denied there was a deal. "Reorganization did not figure in the decision," he said.

Eugene Bergoffen of the National Forest Products Association said of the roadless area decision, "We're relieved there was not a substantial move for more wilderness." However, he said the 15 million acres Carter wants to set aside could force about a 10 percent reduction in projected federal timber sales.

The roadless areas include 2,919 tracts in 35 states and Puerto Rico. The recommendation for 15.4 million acres of wilderness would almost double the size of that system, which is strictly protected from commercial intrusion or motorized activity of any kind.

The new wilderness areas would include 5.5 million acres in Alaska, 2.2 million acres in Idaho, almost 2 million in Colorado and 1 million in California.Several eastern states, including Virginia and West Virginia, would also receive new wilderness.

"For many years, the process of determining the best uses of national forest has been a slow, piecemeal effort," Carter said in a statement."It is my hope that the decision announced today will help resolve the long-standing controversy."

The president said, "We struck a reasonable balance between accommodating the nation's needs for wilderness and for other goods and services produced from these lands . . .

"This will help our national economy as well as the growth and stability of many local communities by providing additional oil and gas, minerals and timber products which are essential to restraining inflation and increasing productivity."

One of the largest potential conflicts in the roadless areas centered on the so-called overthrust belt, a Rocky Mountain region with considerable oil and gas potential. Ninety-five percent of the area was excluded from wilderness proposals and will thus be open to exploration, Cutler said.

Of the 36 million acres now open to potential commercial use, only a small portion will be developed this year, he added. However, land use plans for the entire area should be completed in five years.

Last week, 217 enviromental groups, including many local organizations that arose to save specific areas, wired Carter to protest the impending decision. The Wilderness Society's executive director, William A. Turnage, called it "among the most negative decisions in the history of public land management and one which threatens to negate the administration's impressive environmental record."

"As a result," Turnage said, "60 percent of the untouched remnants of America's national forests will be available to entry by logging and mining interests even though this controversial acreage contains inconsequential commodity conflicts and is of demonstrated high wilderness quality."

Whether to present the wilderness proposals in one bill or several remains to be decided, Cutler said. It will probably take two or three Congresses before all 15.4 million acres is set aside, he said. However, the Forest Service can open the 36 million acres to development by administrative order.

The most controversial area are in Washington and Orgeon, where environmentalists say some of the nation's most beautiful wild mountains and valleys will be logged. The Pacific Northwest and southeast Alaska contain the nation's most productive timberlands.

The Interior Department's Bureau of Land Management is also reviewing vast roadless areas for wilderness designation. However, decisions on individual areas will be made on a piecemeal basis over several years.