IT IS RARE when great numbers of loggers and backpackers agree on what should be done with any of the untouched lands of the West. It has happened in central Idaho. Last week, with relatively little dispute, the Senate voted to set aside 2.2 million acres of federally owned land there as the River of No Return Wilderness.

There will be more bargaining as the bill moves through the House. Some of the backpackers would like to see a little more land added to the wilderness area. Some of the loggers would like a smaller set-aside -- some mining companies would like to have better access to the cobalt believed to lie under one part of the wilderness. But, except for minor adjustments, a compromise has been reached that will preserve in its pristine state some of the nation's most spectacular land.

The area involved is the largest single tract in the continental United States ever designated as wilderness -- about the size of Yellowstone National Park-- and covers almost 5 percent of the state of Idaho. It includes the best of the Salmon River country where mountains, sparkling streams and wildlife of many kinds abound. The area has remained unspoiled because of its inaccessibility until recent times; the Salmon did not become known as "the river of no return" without reason.

The legislation creating this new wilderness is the first to emerge from the long evaluation of the nation's remaining roadless area. While it would be foolish to expect other legislation emerging from that study to encounter as little effective opposition as this one has, the people of Idaho have set a useful precedent by working together to set its general outline. The River of No Return Wilderness may well become to the nation's wilderness system what Yellowstone, Yosemite and the Grand Canyon are to the park system.