Scientists studying mummies in Egypt have long believed that the first cases of the crippling virus poliomyelitis date back 5,000 years.

Now, World Health Organization officials say, the birthplace of polio has apparently for the first time ceased to be a source of transmission of the virus, with no new cases recorded in Egypt over the last 12 months. The officials described it as a key milestone in the effort to eradicate the disease.

The health organization, pending a final review in the coming days, is expected next week to announce that Egypt will join almost the entire world in proving that they no longer have reservoirs of the virus.

Before the WHO Executive Board earlier this week, WHO Director General Lee Jong-wook said that no new cases in Egypt over the last year was cause to celebrate. ''We are at the threshold of a polio-free world," he declared.