CAIRO -- Eroded by time, plundered by grave robbers, assaulted by air pollution, the pyramids have taken their knocks over the centuries. But now they may be facing the gravest threat of all: urban sprawl.


To the alarm of archaeologists and United Nations cultural authorities, the Egyptian government is building an eight-lane highway across the desert plateau that includes the site of the three pyramids of Giza -- one of the world's most famous tourist destinations, and the home of the Sphinx. Critics say a land rush is sure to follow.


The new highway, if completed as planned, will pass within about two miles of the Giza pyramids. It violates both Egyptian law and an international convention protecting such globally significant sites, according to Said Zulficar, director of safeguarding activities of the cultural heritage division of the UN Educational, Scientific and Cultural Organization.


Other encroachments include high-rise buildings, housing projects, two garbage dumps, military barracks and a military factory "belching filthy black smoke," Zulficar said in a telephone interview from UNESCO headquarters in Paris.


"The problem is, you turn a pristine desert archaeological site into an urban site like the Acropolis in Athens, which is surrounded by buildings," he said. "There will be hotels, restaurants, gas stations. It will lose its uniqueness."


The Egyptian government has never been accused of overzealous zoning. Haphazardly and often illegally built apartment houses block the pyramids from view on the main road approaching from downtown Cairo, and a warren of tourist shops selling perfumes and paintings on papyrus sprawls to within a few hundred yards of the Sphinx.


The new road, a bypass route on Cairo's southern side, would, if completed, cut off the last expanse of empty desert that remains contiguous with the Giza pyramids, which are already hemmed in by development on two sides. Zulficar said when he raised the matter with Egypt's culture minister and other senior officials, they told him they were unaware of the intrusion and would consider options for stopping it.


On a tour earlier this month, Zulficar found that the highway cuts through the protected zone, a strip of desert that encompasses both the Giza plateau and the lesser-known Dahshour pyramids, about 17 miles to the south. Construction is now nearing the immediate area of the Giza pyramids.


"I was horrified to see what I saw," he said. "The thing is practically finished. It's in total violation of the world heritage convention they signed, and it's in violation of Egyptian law."


Although the government has yet to make public a map of the new road, "there already are private homes going up" along the completed portion, Zulficar said.


He found numerous other encroachments, some in the protected area and some in a buffer zone, where buildings are theoretically subject to strict height restrictions. "There are 3,000 housing units being built right on the fringes of the zone," he said. "There are six-story-high buildings. There's a palm grove that is being cut down. There's a huge police housing complex being built a kilometer from Cheops," the largest of the three pyramids.


Zulficar has asked the director general of UNESCO to appeal personally to Egyptian President Hosni Mubarak to remove the encroachments.


Zahi Hawas, who directs archaeological activities at the Giza pyramids, said he found no archaeological ruins in their path. He added, however, that he was not involved in the decision, and hopes it can be reversed in light of the rapid development that is already occurring in the area.