The trackless deserts of southwestern Egypt, one of the most remote regions on earth, are beginning to yield their secrets.

American and Egyptian scientists linked by satellite to communications facilities in Greenbelt, Md., have completed a 12-day trek through the region. They found major iron ore deposits, prehistoric cave paintings of African wildlife, tools and artifacts of the people who lived there when the land was fertile, and new information about the way deserts are formed.

From Kharga oasis, south of Assiut, the scientists traveled by jeep and dune buggy to Jebel Uweinat, a hill that rises near the point where Egypt, Libya and Sudan meet, a distance of almost 500 miles across sand dunes, rocks and craggy valleys created by rushing water in an earlier geologic age.

But the land is so little known and so poorly mapped that the scientists do not know exactly where they were. They will find out only when they see the charts of the signals they transmitted each day to U.S. Nimbus 6 satellite. From these they can determine what their positions were when the transmissions were made.

A local guide accompanied them, but participants said he was of little help in navigation because he is accustomed to crossing the desert at a camel's pace, judging location by time of day, and was disoriented by the speed of motorized travel.

The leader of the expedition was Farouk Baz, Egyptian-born research director of the Center of Earth and Planetary Studies at the Smithsonian Institution in Washington.

The trek, he said, was "unbelievable, the best trip of my life. We're talking about an area that covers one tenth of Egypt and everywhere you stop you see something significant - something that tells you about climatic change or the movement of sand or pre-Neolithic settlements or mineral deposits."

Among the descoveries, he said, were:

Hand axes, grindstones, spearheads and the shells of cooked ostrich eggs clustered around depressions ago. Carbon dating of the eggshells, that were probably lakes millennia he said, will reveal when they were cooked, thus making it possible to say when man lived in the region.

"Lovely cave paintings" of baboons, giraffes and other animals now found only south of the African Sahel desert, and paintings of faces with black African features.

"Fabulous examples of things that will help us understand Mars." Satellite photos had shown the area to be intriguingly similar to areas on the planet Mars as photographed by the U.S. Viking spacecraft, and geologists in the expedition hope that by analyzing the wind and erosion patterns they found in the Egyptian desert they can learn more about the Martian surface.

An eight-mile-long deposit of good quality iron ore, exposed by the desert winds that have worn away the covering rock. Egypt is self-sufficient in iron ore, but Baz, a geologist by training, said there was more than enough to be commercially exploitable when present supplies dwindle.

Near the Sudanese border the scientists met a camel caravan of Bedouin traders making their 40-day trek to Egyptian markets with a salty substance called trona, which is mixed with chewing tobacco. "They were shocked and so were we," Baz said of this chance meeting in the empty wasteland.

Daytime temperatures went up to about 120 degrees Fahrenheit, Baz said, and the only living things the scientists met, aside from the caravan, were one scorption and a few foxes that left tracks in the sand camp one night.

The 33-man expedition brought back nearly three tons of material for study, Baz said, but to him the most important result of the trip was a conclusion which he expects to cause furious argument within the scientific community.

The conclusion he said, is that the activities of man have little to do with the creation of deserts.

"Deserts are made by God, not man, and the effect of man on the process is minimal," he said.

Baz said the United Nations and other organizations are wasting millions of dollars on programs aimed at preventing overgrazing and deforestation in the belief that these contribute to the encroachment of desert onto arrable land.

"You can see it in the rock," he said. "It wasn't grazing by goats, eating away the shrubs, but erosion by the wind that did it." He said grasslands once flouriched in what is now the Egyptian desert and were destroyed not by man but by wind that dried up the water supply and eroded the soil and rock.

Nearly the Libyan border, he said one can actually see the hot wind form a vortex that eats away at the rock, gradually reducing it to more sand. The natural structures most resistant to this process, he said, are those with tapered tops, and he speculated that this phenomenon may have inspired the ancient Egyptians to develop the pyramid.

Baz said the papers prepared by the archeologists, botanists, geologists and geographers in the expedition will be published as a book next year. The artifacts, he said, probably will be housed in a museum in Kharga.

Egypt is 96 per cent desert. For centuries the Egptians, drawing sustenance from the Nile, simply ignored the desert, but there has been a sudden interest in it recently.

Oil exploration, overcrowding of the Nile valley and the prospective recovery of the Sinai Desert from Israel have combined to stimulate academic and scientific research into the possibility of putting the empty wastelands to practical use.

In the southwest, Baz said a few of the remote valleys have enough ground water to support shrubs and tamarisk trees, but there is no record of any rainfall for 20 years. The scientists concluded, he said, that there was no possibility of reclaiming any of that part of the country for agriculture.

In fact, satellite photography and an earlier expedition by Baz into the nothern part of the desert, closer to the Mediterranean coasts, have shown that Egypt - far from reclaiming the desert - is literally losing fertile grounds to the advancing sands.