Mr Christopher was told by Syria's Foreign Minister, Farouq al-Sharaa, that President Assad was "not available", a State Department official said. The refusal to meet Mr Christopher, whom he saw twice the day before, suggests Syria's leader is dissatisfied with US mediation.
Having failed to see President Assad, Mr Christopher intended to fly to Beirut, but was stopped by advice from General George Joulwan, the commander of US and Nato forces in Europe, that the trip was too dangerous. Nicholas Burns, the State Department spokesman, said: "Five minutes before leaving the hotel, the Secretary [of State] received the red light."
US officials made light of the rebuff by President Assad, saying Mr Christopher's party arrived in Damascus behind schedule and the Syrian leader was already committed to a meeting with Benazir Bhutto, the Prime Minister of Pakistan.
The abortive trip to Lebanon would have involved Mr Christopher flying to Cyprus and taking a helicopter to Beirut. General Joulwan was reportedly aware of a specific threat to the US party.
Syria wants to return to the 1993 understanding in Lebanon whereby Israel and Hizbollah, the Lebanese guerilla movement, pledge not to attack each other's civilians. Shimon Peres, Israel's Prime Minister who faces an election in five weeks, wants to show the bombardment of Lebanon has produced results for Israel.
He wants immunity from attack by Hizbollah for Israeli troops in the occupation zone in south Lebanon and greater freedom of action for Israeli forces to fire into villages deemed hostile.
Earlier in the day in Jerusalem, Mr Christopher had sounded more optimistic as he showed Mr Peres a one-page document, presumably outlining peace proposals.
The fighting in Lebanon overshadowed the meeting in Gaza of the Palestinian parliament-in-exile, the first time it has met on Palestinian territory. Leila Khalid, the former hijacker, boycotted the first session, saying: "I received a call from my sisters in Lebanon ridiculing my return and saying that they are being displaced."
Mrs Khalid sat outside the hall in the centre of Gaza City as Yasser Arafat, chairman of the PLO, told the Palestinian National Council the time had come to amend its charter. He has already agreed that clauses calling for the destruction of Israel should be removed.
Mr Arafat called on the parliament to "to amend all articles that contradict the peace of the brave". He said this would strengthen the Palestinians "negotiating position and remove the pretexts with which the Israeli government is armed."
It is not a view endorsed by all members of the parliament, which claims to represent 4 million Palestinians abroad as well as 2.3 million in the West Bank and Gaza. Mrs Khalid told the Independent that her group, the Popular Front for the Liberation of Palestine, opposed "changing the charter, as this is against the goal of our people. We cannot change it until Israel recognises our national rights".
There is little doubt Mr Arafat will get what he wants. Under the terms of the latest Israel-Palestinian agreement the council must amend or revoke the charter by 7 May. Mr Arafat hopes it will speed up Israel's partial pull-out from Hebron.