Just as high-level diplomacy to end the conflict over Kosovo was starting to work, NATO had to go and bomb the embassy of a country without whose approval there can be no United Nations force to replace the air strikes. It was the fault of the CIA, we are told, which identified the wrong building, but NATO says the bombing will go on.

As the news of the bombing of the Chinese embassy in Belgrade reached Washington, the initial shock and dismay were quickly replaced by determination to see the NATO air campaign through until President Slobodan Milosevic cracks.

Some in the Clinton administration, while deploring the disastrous error in targeting the wrong building, see the mistake as lending urgency to the move towards the peace agreement in which Russia is now playing a key role. "We will just have to ride it out," a senior administration official told the New York Times.

President Clinton, who was touring the scenes of devastation in Oklahoma following last week's tornadoes, reacted sharply to the condemnation by China and Iraq of the embassy bombing as "barbaric".

"What is barbaric is what Mr Milosevic has done. What is barbaric is the intentional ethnic cleansing he has provoked," Mr Clinton retorted. "I hate this but someone, some time, has got to stand up against this sort of ethnic cleansing."

The President appealed for "a sense of proportion here" as there have been more than 10,000 bombing sorties since March 24th.

While the resolve of President Clinton and his national security aides to press on with the bombing seems clear, the destruction of the Chinese embassy at this point in the campaign is just as clearly a diplomatic and public relations disaster. But it is not irretrievable.

China called a midnight meeting of the UN Security Council to denounce the bombing, and the acting US ambassador, Peter Burleigh, had to listen to stern criticism from China, Russia, Iraq and other countries. The Chinese ambassador, Qin Huasun, called it a "crime of war that should be punished", but was not able to persuade the council to condemn the US.

In the coming weeks China's co-operation will be sought by the other four permanent members of the council, the US, Russia, Britain and France, as efforts are stepped up to draft a UN resolution which will bring an end to the NATO campaign and allow the return of the estimated one million displaced Albanian Kosovans with the approval of President Milosevic.

The bones of this peace formula were put in place last week by the foreign ministers of the G8 - the biggest seven economic powers and Russia - whose special Balkans envoy, Viktor Chernomydin, is acting as intermediary between NATO and Belgrade. While conceding that his diplomatic task is now more difficult he is pressing ahead.

There is still the huge problem of NATO's role in the international force which will ensure the safety of the Kosovans as they return to their homes. This was fudged in the G8 statement last week, but the US seems confident that Russia now accepts a NATO presence will be necessary and that it will be Mr Chernomyrdin's task to persuade Mr Milosevic to drop his opposition to this.

China is naturally enraged by the embassy bombing but would find it hard to use its Security Council veto to block the kind of peaceful solution which it has advocated while calling for an end to the NATO air strikes.

While the US is thus putting a brave face on the embassy bombing and pressing ahead with its NATO allies in mixing air strikes with diplomacy, it remains to be seen if President Clinton will continue to carry the country with him. Already the public support for the air strikes was slipping compared with six weeks ago when it began.

The pictures of a besieged US embassy compound in Beijing this weekend as Chinese demonstrators vent their anger are not reassuring to an American public.

The scepticism over the effectiveness of air strikes without the backing of ground forces is likely to increase as a result of this embarrassing mistake. How reliable are the daily NATO reports of damage done to the Serbian forces dug in in Kosovo if intelligence could not identify a building in central Belgrade where NATO country diplomats used to attend cocktail parties?

President Clinton must also be seriously concerned about the conflicting signals he is getting from Capitol Hill which have baffled even the most experienced Washington observers. In the past two weeks the House of Representatives has refused to declare war on Yugoslavia or vote to stop it; has refused to support the air campaign; has refused to authorise the President to send in ground troops without Congressional permission; and has then doubled the amount of money he requested to fund the air strikes.

The Senate in its turn has rejected an attempt to allow the President to use "all necessary force" in Yugoslavia, with both Democrats and Republicans against such a move. The White House itself also lobbied against the move, which it correctly saw as an attempt by a handful of senators to force the President's hand and prepare for a ground war.

But President Clinton, a reluctant warrior at any time, is determined not to go the way of the Vietnam War and send US troops into action. The air strikes are the only way and mistakes like the Chinese embassy will have to be accepted as an unfortunate accident.

You have to "keep the big picture in mind", was the message of Ambassador Burleigh to the UN Security Council and of Washington this weekend.

For the experienced Washington Post commentator, David Broder, there is another less inspiring picture in view at the moment. "The nation and the world are learning what it means for the United States to conduct a war with a weak-kneed Congress and a wobbly President. It is not an inspiring spectacle."