The clear, burbling waters of Chinchihuapi Creek flow out of misty hills, past dark stumps of an ice-age forest and through green pastures, where cattle graze and from time to time a farmer still finds a huge mastodon tusk eroding out of the peat. No one standing by the creek today would suspect that this bucolic place, known as Monte Verde, was so recently the scene of a pitched intellectual battle among archeologists over when people first inhabited the Americas.

The scars of excavation have disappeared. Lush grass grows over the filled-in trenches, where archeologists had found the amazingly preserved wood, tied and knotted strings, hearths and even leftover mastodon meat of an ancient hunter-gatherer camp. The cookhouse and tent sites of the excavators are also gone without a trace.

Even the scars of battle seem to have healed. Last year, after two decades of acrimony, a blue-ribbon group of archeologists reached a kind of peace treaty acknowledging the triumph of the Monte Verde excavators. Their evidence had indeed established the site as the earliest firmly dated place of human habitation in the Americas. People had lived here 12,500 years ago, about 1,300 years before the previously accepted date for earliest known Americans, derived from stone spear points found in the 1930's near Clovis, N.M.

On a recent visit to Monte Verde, east of this seaport in southern Chile, Dr. Mario Pino, a geologist at the Southern University of Chile in Valdivia, leaned into the north bank of the creek and stabbed the dark soil with the pick end of a geology hammer. He exposed more pieces of wood from the camp where prehistoric humans once lived.

But the wood held less interest to him than a green knoll several hundred feet away, south of the creek. Pointing with the hammer, Dr. Pino said that cursory excavations there had turned up possible remains of human habitation at Monte Verde 20,000 years earlier than the camp north of the creek. Should this prove true, it would revolutionize research into one of the most intractable mysteries in American archeology: Just when were the Americas first truly a New World, and how did people get here?

Dr. Pino and Dr. Tom D. Dillehay of the University of Kentucky in Lexington, the archeologist who has directed the Monte Verde explorations, are planning more extensive excavations of the knoll site in January 2001. They plan to strip away six feet of topsoil with a bulldozer, then begin fine- tooth digging in the lower layers where evidence of human activity has emerged.

"There's no doubt about the age -- it's 33,000 years old," Dr. Pino said of the sediment layers bearing the apparent artifacts under the knoll. The date, which would put the occupation during a warm interlude in the ice ages, is based on radiocarbon examination of burned wood that scientists suspect came from hearths at the hunting camp. Archeologists found the charcoal in three shallow depressions lined with scorched clay. Other hints of human occupation include 24 fractured pebbles, several of which were probably flaked by people using them to cut and scrape meat, hides and plants.

When independent archeologists visited Monte Verde last year and authenticated the younger camp site, Dr. Pino said, they also examined the material from the deeper, 33,000- year-old layer. "They said there is no doubt these are real human artifacts," he said. "We were surprised. We expected another fight."

Dr. Dillehay is somewhat more circumspect. In an interview by telephone, he said: "We'll open up that level and see what's there. If the results remain ambiguous, we will have done the best we could. But I'm leaning toward accepting the antiquity of the level and the traces of human activity."

Dr. David J. Meltzer, an archeologist at Southern Methodist University in Dallas, who was a member of the review committee that endorsed the younger site, welcomes the new excavations. The older layer is "really intriguing," he said, "but we can't conclude anything about it until we have a better sense of what's there."

What is needed, Dr. Meltzer said, are excavations over a much larger area to increase the chances of finding many more artifacts and samples for radiocarbon analysis. If these support the date and the presence of humans at the site, he predicted, other archeologists wll be quicker to accept the findings than they were with the first Monte Verde site.

"Of course, it depends on what they find," he said, "but this time archeologists wouldn't be as resistant because now they are not operating within the framework of Clovis history."

Since the 1930's discovery of distinctive spear points of the so-called Clovis hunters, nearly all archeologists staunchly held the view that the first Americans were big-game hunters who crossed the ice-covered Bering Straits between Siberia and Alaska about 12,000 to 13,000 years ago -- that is, not long before the 11,200-year-old dates of the earliest Clovis weapons. Prior to the Monte Verde breakthrough, several other presumed pre-Clovis sites had been reported, but none has yet met all the requirements to be judged an authentic human site dating earlier than the Clovis people.

Once archeologists accepted the 12,500-year date for the younger Monte Verde camp, they were forced to rethink how long people had already been in the Americas for them to have made it all the way from North America to southern Chile, 500 miles south of Santiago.

Archeologists are also puzzled by the absence so far of any confirmed human sites in North America that predate Monte Verde. The numbers of migrating human bands must have been so small, and their movements so nomadic, that they left no impression on the land they were "archeologically invisible."

No scholars seriously consider the possibility that the early Americans landed first in South America. All linguistic, genetic and other evidence points to the Bering Strait as the most likely point of entry.

"But now we realize we don't really know when the human entry time was," Dr. Meltzer said. And Dr. Dillehay said he did not even want to speculate on the implications for early American migrations if he should establish that people were at Monte Verde as early as 33,000 years ago.

If it had not been for a quirk of nature, Dr. Pino pointed out, archeologists would probably never have known that some hunting-and-gathering people occupied the banks of the Chinchihuapi at least 12,500 years ago. The land covering the site is a water-saturated peat bog, which isolated the wooden poles and tent-pegs, animal hides and other perishables of the old camp from oxygen and thus decay. Otherwise such materials rarely survive the centuries.

The attention of archeologists was first drawn to Monte Verde by the chance discovery of some mastodon bones. The owners of the land, Juan Barria and his son, Sergio, led Dr. Pino across the squishy bog to a shed to show him their latest find. It was a piece of mastodon tusk, which would have been 6 to 10 feet long and 6 inches in diameter.

"This animal would have weighed two tons," Dr. Pino said, rubbing the tusk. "Enough food for two or three months for a prehistoric family living at Monte Verde."