Anthropologists have found the footprints of two human-like creatures who walked the earth 3.6 million years ago, antedating by at least 400,000 years any fossil footprints before.

The two separate sets of footprints were found in East Africa in a volcanic bed preserved by fallen ash and then eroded by rainfall over time. The footprints were uncovered in the Laetoli region of northern Tanzania by a team of anthropologists led by Dr. Mary D. %leakey, who called it "another important piece of evidence" in the search for the origins of man.

Fossil bones of what are believed to be early man have been found that are as old as 3.6 million years but the oldest footprints heretofore went back only 3.2 million years. The importance of the discovery of footprints is that it is proof that a man-like creature was already behaving like a man and not like an ape.

"Early man reached a free, upright bipedal gait 3.6 million years ago," Leakey said yesterday at a news conference at the National Geographic Society, "We have now established that without question."

The fossil bones from the same time period suggest that man's brain had not yet expanded to the size it is today, but Leakey pointed out that brain expansion almost surely followed man's emergence as an upright walker.

"Walking released the hands for other activity," Leakey said. "With the hands freed, the brain expanded to meet the tasks that could be done with the hands."

The footprints were uncovered last year by the University of Rhode Island's Dr. Paul Abell, who was quarrying a block of rhinoceros tracks when he noticed the print of a human-like heel. On removing the overburden, Abell found a trail 73 feet long made by two individuals.

One set of footprints was larger than the other. The two sets never overlapped, suggesting they had been made hours or even days apart. The smaller footprints were flatter and deeper, suggesting the smaller creature might have been carrying a child.

"The smaller creature made a halfturn to the left at one point, as though she heard or saw something," Leakey said. "It gives the whole thing a very human aspect."

Leakey referred to the smaller creature throughout the news conference as "she" and "her." That creature's footprint was almost two inches smaller than the other's.

The two creatures started out using a long stride, Leakey said, then shortened their gait before making several small turns. One set of prints was made on a dry surface, the second set in a damp surface. This indicated to the anthropologists that the creatures were not walking together.

The footprints were preserved by a rain that fell just before or during the making of the second set of prints. The rain "consolidated the ash," Leakey said. "It was almost a unique set of circumstances."