There are few places on earth where the achievements and aspirations of antiquity are more awesomely visible than in the Nile Valley of Egypt, where the monuments of Pharaonic civilization form a direct link with the origins of the Egyptian nation 50 centuries ago.

Unfortunately, shockingly, those monuments are eroding. Tombs, temples, hieroglyphs and inscriptions that have survived conquest, vandalism, extremes of climate and the replacement -- first by Christianity and then by Islam -- of the faith they symbolized are crumbling and flaking before the onslaught of groundwater, air pollution, technology and the feet of tourists.

Both aspects of Egypt's ancient heritage are effectively explored in "Egypt: Quest for Eternity," a National Geographic special at 8 tonight on Channel 26.

In the best National Geographic tradition, this documentary combines imaginative color photography and lucid, relatively restrained text to provide a useful introduction to the religion and art of ancient Egypt and to the current efforts of American archeologists to preserve them.

At Luxor, site of ancient Thebes, the epigraphic survey of the University of Chicago has been at work for nearly 60 years at the painstaking task of making facsimile -- three-dimensional drawings of the inscriptions and pictures on the great temples. These are, says narrator Richard Basehart, "the only record that will remain when the hieroglyphs and decorations have disappeared forever."

Another team, from the University of California, is shown using aerial photography and computer data to create the first comprehensive map of the necropolis of the west valley, across the Nile from Luxor. These are labors of love as well as scholarship, and photographer-director Norris Brock has captured their scope by taking cameras to sites never before accessible to television.

The most dramatic film shows the dismantling of the great temples at Abu Simbel by workmen racing the rising waters of Lake Nasser, behind the Aswan Dam, and their reassembly on higher ground. But that is an old story; what is new is the careful reporting on the erosion of the drawings and inscriptions and the apparent certainty that they will soon vanish into history.

The strongest point of writer-producer Miriam Birch's script is its lucid if cursory explanation of the religion of ancient Egypt. The artifacts of Tutankhamen's tomb and the monuments built by Ramses II are part of a coherent culture in which religion and state power intertwined, a culture to which this documentary offers a useful introduction.

If the program has a failing, it is in the few sanitized glimpses of contemporary Egypt. While it was not the purpose of this program to depict the problems of health, nutrition and housing that beset Egypt today, it was not necessary to gloss over them entirely. Anyone who has visited the pyramids, for example, will know it is misleading to show them without the crowd of hawkers, tour guides, vendors and beggars who besiege the unwary tourists.