The Washington Post yesterday refused to sell advertising space to the Iranian government for a half-page "Christmas Message to the Christian World" from Ayatollah Ruhollah Khomeini.

The Post rejected the advertisment because it referred to the 50 American hostages held in the U.S. Embassy in Tehran as "spies and traitors."

"[The advertisement] is potentially libelous. But in addition to that, we simply do not accept serious charges against people that are not substantiated. It is a matter of policy," said Christopher Little, vice president and counsel for the newspaper.

Little said yesterday that he told officials at the Iranian Embassy in Washington that The Post would run the advertisement if the words "spies and traitors" were deleted from the message.

But Hossein Ava, press attache for the Iranian Embassy, said the words in the message were those of Khomeini and could not be changed without his permission.

Ava complained yesterday that The Post did not have the right to reject the advertisement. "This is not the message of an ordinary person. It is the message of Imam Khomeini to the people of the world on Christmas Day," Ava said.

Courts in the United States have consistently ruled that newspapers have the right to reject advertisements without explaining why. The Post on Sunday printed a full-page advertisement from Princess Ashraf Pahlavi, sister of the deposed shah, Mohammad Reza Pahlavi. The advertisement, addressed to United Nations Secretary General Kurt Waldheim, defended the shah's regime and attacked Khomeini's rule.

The Iranian Embassy, which received Khomeini's Christmas message at noon yesterday, attempted to place the advertisement only in The Washington Post, according to Ava. He said the embassy will try to place the advertisement in other newspapers today.