Prince Charles has told a London weekly magazine that he was beaten twice as a schoolboy.

In an interview with Radio Times, the prince said he was beaten by the headmasters at Cheam, a private boarding school for boys between the ages of 8 and 13. He said the school had two headmasters. "They took turns at beating us. I was beaten twice," he said.

He did not say how he was beaten, but most schools like Cheam use a cane or rubber-soled gym shoe to administer corporal punishment.

Prince Charles said he was beaten for "ragging [hazing] in the dormitory and things." He added: "I didn't do it again. I was one of those people for whom corporal punishment actually worked."

One of the headmasters named by Charles, Peter Beck, has been invited to the royal wedding on Wednesday. Chicagoan Threatens Prince

A former Chicago police officer was held yesterday on $30,000 bond after he allegedly threatened to assassinate Prince Charles, federal authorities said.

John Valkenburg, a member of the department's now-disbanded Intelligence Unit, was arrested Thursday after he allegedly said he planned to travel to Washington, D.C., yesterday and continue on to Great Britain to "get Prince Charles."

Valdenburg was charged with threatening to assault an internationally protected person and is to be arraigned Tuesday, officials said.

Assistant U.S. Attorney Ira Raphaelson said U.S. Magistrate James T. Balong ordered Valkenburg to undergo a psychiatric examination. Queen Mother III

Queen Mother Elizabeth was "improving" yesterday after three days in bed with a fever, a spokesman at her Clarence House residence in London reported.

It remained uncertain, however, whether she will be able to attend the wedding of her grandson Prince Charles and Lady Diana Spencer Wednesday.

The queen mum, as she is called in England, will be 81 on Aug. 4. She has canceled all engagements until the wedding, the spokesman said.