The seizure of the American hostages in Iran sent historian George Michanowsky looking for evidence of a tradition he was confident he would find -- that holding diplomats hostages has been practiced, and condemned, since man's earliest era.

Michanowsky, a historian of astronomy and the author of a book, "The Once and Future Star," had looked in vain through archives of the Sumerians, who developed man's earliest writing system sometime before 3,000 B.C.

Then he searched through later Akkadian tablets and uncovered the oldest-known warning against the taking of hostages, found at the ruins of Urin Mesopotamia, which is in modern Iraq close to the Iranian border.

The badly damaged 4,000-year-old clay tablet from Ur carries the warning written in cuneliform symbols: "Mary Shipria La Takaliam," or "Do not detain my envoy." The author and the recipient are lost in time, but Michanowsky, who dug a transcription of the fragment out of the achives at the New York Public Library, presumes that one petty ruler wrote it to another.

The point of his research, Michanowsky said, is a that the principle of free movement by diplomats was established at the birth of civilization and those rulers who abused envoys were criticized.

"What's the matter with the king of Assyria that he detains your envoy?" reads a table found in what today is Turkey, Michanowsky said.

"Envoys will establish good relations between hostile rulers," reads another tablet that he cites as evidence of the general reliance our early ancestors placed on the free movement of diplomats.

The Akkadian-speaking people adopted cuneiform writing from the Sumerians for their own language, and Akkadian tablets became a widely used medium of diplomatic communication in the Near East, Michanowsky said.

The discovery of Akkadian cuneiform tablets in Egypt in the 19th century led to another revelation with a modern echo. This archive (which also gave clues to the identity of Tutankhamun) contained tablets bearing on Egypt's dealings with smaller, weaker peoples.

Michanowsky said the less powerful leaders constantly complained to Egypt. In effect, he said, their complaint was that Egypt had set itself up as the world's policeman and yet wasn't sending them help when they needed it.