Mrs Harriman, 76, the former daughter-in-law of Sir Winston Churchill, was taken ill while swimming in the pool at the Ritz Hotel. Her son, the Conservative MP Winston Churchill, flew to Paris to be at her bedside.
President Jacques Chirac asked the foremost French surgeons to make themselves available to the American Hospital in the suburb of Neuilly where Mrs Harriman was said to be in a "very serious" condition.
President Clinton, a friend and protege of Mrs Harriman long before he reached the White House, was said to be deeply concerned. "The thoughts of the President and the First Lady are with Mrs Harriman at this moment," a White House spokesman said.
Like no other political personality still living, Pamela Harriman can claim personal acquaintance with most leading figures on both sides of the Atlantic for the past six decades. Born Pamela Digby in Farnborough in 1920, she married Randolph Churchill when she was 19, on the eve of the Second World War. On her divorce at the end of the war, she moved to France, where she was friendly with, among others, Gianni Agnelli, Andre Malraux, and Jean Cocteau. In 1960 she married the Hollywood producer Leland Hayward.
After his death in 1971, she met, and married, the billionaire statesman and political fixer, Averell Harriman, whom she had known during the war.
For 15 years, their mansion in Washington was one of the principal political salons in the US, and the Harrimans among the leading figures and financiers of the Democratic Party. After her third husband's death in 1986, Mrs Harriman continued the role alone, encouraging, among others, the ambitions of a young southern governor, Bill Clinton. She became ambassador to Paris when he became president in 1993.
It was strongly rumoured a year ago that she would relinquish the post at the start of a second Clinton term. The rumour was renewed only this week by Newsweek, which predicted she would be replaced by Frank Wisner, ambassador in New Delhi, or Felix Rohatyn, an economist close to the President. John Lichfield - ParisReuse content