The federal government is preparing to take its first steps toward helping wilderness groups preserve and improve the 2,000-mile Appalachian Trail that stretches from Maine to Georgia.

Within the next three years, the government hopes to buy sufficient land and easements to return to the woods the 181 miles of trail now routed along public roads and highways. Forty-one miles of the "trail" are on roads in Virginia and Maryland.

As of last month, an additional 600 miles of trail remained in jeopardy, where the trail is on privately owned land that hikers can be excluded from at any time, according to the National Park Service and the Potomac Appalachian Trail Conference (PATC). The PATC is a federation of hiking clubs whose 80,000 members maintain "the world's longest marked trail." Some 76 miles in Virginia and 10 miles in Maryland are still privately owned.

Under the Appalachian Trail bill signed by President Carter just over a month ago, the federal government is authorized to spend $90 million during the next three years to widen the existing trail right-of-way and preserve forever the endless wilderness [WORD ILLEGIBLE] path along America's eastern mountains. The trail was first proposed in 1921 by Massachusetts forester Benton MacKaye. Congress has yet to appropriate the money, however.

The first section of Appalachian Trail to be built south of New York was blazed in 1927 by members of the newly formed Potomac Appalachian Trail Club. At least 26 miles of that original trail, once on mountain ridges, now is on public roads. The white blazes that usually are painted on trees to mark the woodland trail are placed on utility poles.

It was here that farmers once had welcomed the occasional hiker. But most of the mountain land has been subdivided and the new owners have built vacation homes, with fences and no-trespassing signs to fend off the increasing hordes of hikers.An estimated 4 million persons a year now make pilgrimages to the Appalachians to hike on the legendary trail.

Although the 2,000-mile trail was officially completed in 1937, blazed almost entirely by volunteers, the job of trail blazing and trail maintenance has been continous. Windy mountain weather and the steady tramp of lug-soled hiking boots erodes the trail, and the boom in second homes in the mountains has forced constant relocations.

To help preserve the trail, Washington-area residents are out every weekend, with pick and mattock, saws, ribbons and white paint. Last year alone the work of volunteer crews on the Appalachian Trail was valued at more than $2 million. "The Appalachian Trail is the single best example of volunteerism in the United States," says David Richie, who heads the Park Service's recently formed Appalachian Trail project office.

In the 1930s, state-owned parks and many private property owners agreed to let the trail cross their land. And in 1938 the Department of Interior agreed to set aside land for the trail within national forests and parks. This informal arrangement continued until 1968, when Congress designated the AT as a National Scenic Trail and authorized $5 million a year to be spent to protect it. But the money was never appropriated and the federal government still has yet to buy any land for the trail. The Virginia legislature similarly voted in 1971 to protect the AT but provided no money and no powers of condemnation to acquire land.

This could happen again with the $90 million Congress just authorized, but has not yet appropriated, "as there's many a slip twixt the cup and the lip," said Trail Conference Director Hank Lautz. But this time Interior has pleaded to protect the threatened parts of the trail by 1979 and already has established a special trail staff and a field office to survey land.

Virginia has about 500 miles of trail within its borders, more than any of the 13 other states the traik passes through, with about 400 miles in federal and state parks, 76 miles privately owned and 39 miles routed along public roads.

The Potomac Appalachian Trail Club maintains 231 miles of Appalachian Trail and more than 250 miles of side trails, as well as building and caring for numerous cabins and shelters and publishing maps and guidebooks to the mountains. Its weekend work parties not only perform the most crucial tasks of the club but have become among the club's most popular outings. Several years ago, work parties hit the trails only once a month. That became once a week and now there are usually two work parties a weekend, often with an overnight at one of the club's quaint log cabins.

Several weeks ago a group of 14 volunteer trail blazers from the Washington area, some club members but others out beating the bushes for the first time, spent a sunny weekend on the hillside opposite Harper's Ferry called Loudoun Heights.

They built a new trail down the steep slope under the guidance of Tom Floyd, who supervises PATC's 500 miles of trails on weekends and on weekdays is chief of employment for the Bureau of Reclamation. Loudoun Heights is the hill from which Confederate soldiers bombarded and then captured Harper's Ferry in 1862, capturing 11,000 Union troops just before the battle of Antietam.

Gun emplacements can still be seen from the hilltop, as can the historic stone and mud-mortared home of Charles M. Johnston, a Veterans Administration lawyer who owns part of Loudoun Heights and is one of the increasingly rare landowners who welcomes hikers.

"I'm not sure how much of that hill I own; it's never been surveyed," says Johnston. "But I enjoy hikers, the long-distance ones and those just out for the day. It pleases me to have them."

His hillside "probably will be bought or an easement purchased for the trail," said trail-builder Floyd, "and so will some land down below where hikers now must walk along busy Route 340 for half a mile." Johnston said he's be happy to sell the land or grant Interior an easement.

With Floyd and other experienced trail blazers you don't have to have prior experience with a pick and matock, the universal trail-building tool. "I'm a real tenderfoot. I don't even know how to roll my sleeping bag," said Mary K. Caldwell, of Bethesda, who recently joined the trail club and was on her first work trip. "But I love to be outside digging in the dirt. I'm in an apartment and there's no place to dig," she said.

It also was the first work party for Mary Gavin, who lives at Dupont Circle and works for a tax lobby. "I couldn't stand to be in town over the weekend . . . and I like the clean fresh air out here and getting a few blisters." She called PATC's downtown headquarters and joined the work party at the last minute. They were spending the night at the club's "loft house" in Harper's Ferry, an old building in the historic district.

"I think we do a better job on the trail than someone who doesn't care what it looks like," said Gavin, resting briefly on her pick and mattock. "In 50 years I can come back up here and say, hey, I built this part of the trail."