If you start walking south from Baxter Peak, the summit of this magnificent, mile-high pile of rocks, and carefully follow the splotches of white paint on the boulders, trees and cow chips along the way, you will one day find yourself at Springer Mountain, Ga., 2,050 miles away.

This is the end of the Appalachian Trail, the world's longest - if not its most famous - marked footpath.

Crossing parts of 14 states, maintained by a volunteer army of 80,000 hiking club members, it is as vital to the country's historic Appalachian region as the Colorado River is to the Rockies or the Grand Canyon is to the desert Southwest.

It traverses the battleground of American independence and looks down on pastoral valleys where the Civil War raged. It cuts through eight national forests and two national parks, climbs the breathtaking White Mountains of New Hampshire and the Great Smokies of Tennessee and North Carolina. It crosses the mighty Hudson, the Delaware and the James, a thread linking mountain people and mountain culture across 2,000 miles of ridges, peaks and valleys.

In some places, it is a misnomer to call the Appalachian Trail either a trail or a footpath. There are stretches, including one near the summit of the Katahdin, where it rises almost vertically, and places where it follows the shoulders of highways, within inches of thundering traffic, and a few where stubborn landowners refuse passage.

But from the southern highlands, through the Blue Ridge and into New England, the trail is used more heavily each year. Motorists stop to walk a few steps to its scenic overlooks. Weekend hikers pitch family tents near its springs. Some of its long-distance hikers go for weeks sleeping on the ground and living on freeze-dried food from their packs, while others drop of the trial frequently to find a soft bed and a restaurant.

Hiking the trial from end to end is an obsession for an increasing number of hikers who set out in Georgia each spring to walk north with spring. The ones who have made it - "2,000 milers," they call themselves - have even taken to having reunions.

Recently a bone-tired Rick Sisson, 30, of Leicester, N.Y., paused a few minutes after reaching the Katahdin summit and tried to explain why he had done it.

"When I reached 30, I had come to a crossroads in my life," he said. "It was a last chance to do something like this, so I quit my job, dropped everything and started. Now I have to go find another job. I'll never be able to do anything like this again, but I am glad I did it."

The National Park Service says that about 4 million people now walk on the trail every year. A decade ago, only 40 persons were known to have hiked the entire distance, but recently the walk from Georgia to Maine has become a dream, and a favorite undertaking of growing legions of serious distance hikers.

Last spring, 1,500 registered at Springer Mountain, intending to walk all the way to Maine this year, and estimates are that as many as 300 could make it before winter closes in on Mt. Katahdin.

The popularity of hiking the whole Appalachian Trail reflects an increasing interest in hiking all over the country. Agencies of the federal government now have about 110,000 miles of public hiking trails. When state-owned and privately owned trails are counted, the country has 280,000 miles of trails available for use.

At least 22 different federal studies on proposed new trails or major additions now are authorized or under way. There is a proposal, for example, for a route across the north country linking the Appalachian Trail with the Lewis and Clark Trail in North Dakota. Another plan calls for completion of national historic trails following the major routes of westward migration. Officials plan to complete by 1986 the Pacific Crest Trail, running from Canada to Mexico. Congress authorized it 10 years ago and it was completely marked in 1972, but 1,000 miles of the 2,460 need further protection, such as the acquisition of land to shield the route from development.

The venerable Appalachian Trail itself will undergo substantial change in the next few years, moving it away from highways, rerouting the path in areas where development already has infringed upon it. Earlier this year, Congress authorized the federal government to spend $90 million to purchase land for a widened corridor and for trial relocation in areas where a state cannot or does not move to assure protection of the pathway.

The Forest Service has established land acquisition offices at Martinsburg, W.Va., Allentown, Pa., and Lebanon, N.H., and started negotiations for property along the 850 miles of trail where more protection is needed -- to keep development from breaking up the trail and to preserve at least the illusion of a "wilderness experience" where civilization has already overrun the mountains. Officials expect their main difficulty will be in acquiring valuable land where the trail crosses through economically valuable valleys.

There are still rare instances when hikers who ignore "no-trespassing" signs can find themselves staring down the barrel of a shotgun. But for the most part, there is a warm and long-standing camaraderie between hikers and the people who live along the trail.

An incredible communications network formed by people moving up and down the trail quickly spreads the word of a friendly postmaster, a good general store, or haven for the night from Georgia to Maine. For every land-owner who closes his property to the trail, there are scores of mountain people who treasure their visits with passing strangers.

The bond was developed long ago by people like the late Grandma Emma Gatewood, a legendary trail character, who hiked the entire route three times, wearing sneakers and carrying her belongings in a sack slung over her shoulder. Often she stayed overnight with friends she met in small communities along the trail. She was already past 65 when she made her first through hike; she was 76 when she completed the trip a third time.

Down through the years, hikers since Grandma Gatewood have learned that they will be welcomed at such varied places as the Waynesboro, Va., fire station and a remote monastery near the east bank of the Hudson in New York.

There are friends along the way like Paschal Grindstaff, the postmaster at Damascus, Va., who still recalls the day nearly a quarter century ago when he met his first hiker bound for Maine.

"I was really impressed," he said, "that a man would put a pack on his back and get out here in these mountains and strike out for Maine."

Every summer, hundreds of packages are mailed to the Damascus post office containing food and supplies for long-distance hikers on their way through. Over the years, hikers have learned that if they arrive after the post office has closed, Grindstaff will cheerfully open up so they can get badly needed supplies.

The Damascus Methodist Church has even bought an old two-story house and equipped it so hikers can stop off, cook a hot meal, and spend the night.

At historic Harpers Ferry, W.Va., most of the long-distance hikers stop at the headquarters of the Appalachian Trail conference. There, they find, in Jean Cashin, the woman at the front desk, the single best souree of information on conditions all along the trail. Cashin knows about the hikers going on ahead, the hikers who have quit, where trees are down across the trail, where springs are dry, where country stores once relied on for supplies have closed.

In the log book she oversees are jubilant notes written by hikers who now believe they can complete their journey; the sad storles of those who have had to give it up because of broken bones, pulled igaments or empty pocketbooks.

"Hello to all my followers," Cindy Ross of Reading, Pa., wrote last month. "My money's gone and soon I will be, too. But I can't feel satisfied knowing that another 1,000 miles of trail are waiting for me... Look for me again in two years."

David Walker, a young man from Greenville, Tenn., was bursting with exuberance when he reached the half-way point at Harper's Ferry:

"I got here last night in a storm; it was 95 degrees and I thought I would drown in sweat... I shared someone's porch during a storm and met a very nice little girl who has no parents and wants me to be her pen pal. I walked all over town singing in the rain.... I feel a part of the system. I have walked 926 miles, but I didn't conquer the terrain or the weather. I walked in harmony with them. This is a way of life in which you find out who and what you really are."

At least one couple was married on the trail this summer. A number of other people started their retirement years hiking its mountains. Young men like Rick Sission took the long walk as a last long opportunity for reflection before marriage and a family. Marathon runner John Avery, 29, broke the speed record by going from Springer Mountain to the Katahdin summit in 65 days, 21 hours, and 15 minutes.

In contrast, there were equally determined Norman Greist of Hartford, Conn., who took 43 years to hike every step of the trail, and Ed Kuni of Wilkes Barre, Pa., who ended his trip in Vermont after Hurricane Agnes destroyed his home, but returned to Georgia and hiked the whole trail the next year.

Another adventure ended on the Appalachian Trail recently. It set no records, but required as much determinatin as the efforts of Grandma Gatewood, John Avery or Norman Greist.

Led by two staff members, six students from the Institutes for the Achievement of Human Potential, a Philadelphia school noted for its unconventional approach to treatment of emotionally disturbed and brain-injured young people, completed the hike from Springer to Katahdin.

The group included Richard Bebee, 26, of Santa Ana, Calif., who was in a coma for three months after a motorcycle accident six years ago; Susan Cameron, 29, of West Palm Beach, Fla., who school officials said was functioning at a 3-year-old level when she was well into her 20s, and Jack Fisher, 21, who spent 10 years in a mental hospital. Helen Milestone, 23, Etienne Schroeder, 18, and John Grife, 21, have similiar backgrounds.

They began walking in Georgia -- with Charles Solis Jr. and Lidwina van Dyk of the school staff - April 8. They pushed into the Smoky Mountains with the temperature dropping into the teens, waded through snow in North Carolina and Tennessee, and spent three days struggling past fallen trees after an Easter weekend ice storm in Virginia.

They withstood blistering days of August crossing New York, and were overtaken by autumn cool in the White Mountains of New Hampshire.

In September they climbed Mt. Katahdin in a stinging-cold rain, a soupy fog and a chill wind.

Helen Milestone alternately sobbed and sang "Over Hill, Over Dale" as she struggled the last 50 yards. Etienne Schroeder fell far behind, our of sight in the mist. The others stood on the summit, yelling until they were hoarse, "Come on Mr. Schroeder, come on Mr. Schroeder." Accompanied by Max Britt, another member of the school staff, Schroeder stumbled the last steps to the summit.

Charles Solis, who walked with them all the way, said that none of them would ever be quite the same again.

The next day, beside a lake at the foot of the mountain, each member of the "Appalachian Trail Challenge Team" was presented a medal. Henry Lautz of the Appalachian Trail Conference gave them a certificate attesting to their accomplishment. Glenn Doman, the director of the school, gave each a warm hug, congratulated them for "heroism in the face of all the elements of nature" and thanked them "on behalf of all the children in the world."