Anthropologists have found the fossil bones of what they believe to be a new species of man 600,000 to 800,000 years older than any previously known.

More than 350 fossil fragments of at least 57 individuals of the newly identified creature were found at sites near Hadar in the Afar region of Ethiopia and near Laetolil in Tanzania during scientific expeditions from 1973 to 1977. The scientists studying the fossils have named the creature "Austral-opithecus afarensis," or "Afar Ape-Man."

"Its face, its teeth and its brain were primitive, more ape-like than human,"said the Cleveland Museum of Natural History's Dr. Donald C. Johanson, who has been studying the fossils with Dr. Timothy D. White of the University of California at Berkeley. "But the anatomy below the neck shows an upright, bipedal creature we can definitely place in the zoological family of man."

The "hominid" creature lived sometime between 3.6 and 3.8 million years ago, based on careful age-dating of the rock that served as the creature's burial grounds. The two sites where the creatures' fossilized remains were found lie about 1,000 miles apart, meaning that the creatures were probably nomadic in nature.

Some 22 of the individuals were found at the Tanzanian site, the other 35 were discovered at the Afar site in Ethiopia. The hominid bones at the Tanzanian site were recovered by Dr. Mary Leakey; the Ethiopian fossils were found by Johanson. The University of California's White took over the scientific study of the Tanzanian fossils.

"This species fills in what had been a total gap," Johanson said by telephone from the Cleveland Museum. "It moves the hominid species firmly back in time to between 3 and 4 million years."

"Prior to these findings, the 3-4 million year span of time was a blank for students of human evolution," White said. "Australopithecus afarensis gives us a glimpse of a creature that was ancestral to all later forms of humankind."

Though they named the creature after the Afar site in Ethiopia, Johanson and White said the bones found in Tanzania were the oldest. The Ethiopian fossils were beween 2.9 million and 3.2 million years, the Tanzanian fossils ranged from 3.6 million to 3.8 million years.

Putting the bones back together, Johanson and White described a creature no taller than four feet. Males were all "substantially larger" than females - "a condition," White said, "similar to that seen in modern African apes."

The collection of 22 individuals from the Afar site is one of the largest single finds of ancient man anywhere in Africa, including the finds made at the Olduvai Gorge in Tanzania, which has been described as the "cradle of man." The bones were found along the shores of an ancient lake, whose bed had been exposed in recent years by torrential, seasonal rains.

At least 13 of the Afar individuals were found on a hillside where they may have perished together in a flash flood. There were no marks on any of the bones and there were no animal remains anywhere nearby. The fossilized bones of pigs and elephants were found with the other hominid bones at Afar.

The findings of a new species of hominid are the oldest evidence of what Johanson calls "human bipedal walking." Many anthropologists believe that one of the most critical periods of human evolution was when man's ancestors began to walk.

"It freed the hands and arms for tool-making carrying food and carrying babies," Johanson said. "It also permitted our ancestors to stand upright so they could see over the tall grass of the open plains to search for food and keep watch for predators."

It also set the stage for the next critical step in evolution, which was the gradual expansion of the brain beyond chimpanzee-size to human size. When this happened, man and ape parted company forever.