Then Mrs Blair took the platform at the end of the room and made a passionate appeal for the plight of children abducted and taken abroad by estranged parents. This was not just another summiteers' reception, it was the launch of a children's charity set up by the British Ambassador's wife, Lady Meyer. "Very New Labour," one diplomat said disapprovingly.
Delegates at the Nato summit were all too aware of how it would look if they were seen guzzling champagne while discussing the plight of ethnic Albanians forced to flee their homes in Kosovo. The celebrations for this 50th birthday party were dramatically scaled back, and the emphasis of those which went ahead was on worthiness.
The politicians and their aides did get to a few parties - Bill Clinton hosted a dinner for leaders and their wives at the White House on Friday night, while Madeleine Albright and William Cohen organised a similar event for foreign and defence ministers at the State Department. And the mayor of Washington gave a glitzy reception for delegates at the National Building Museum on Saturday night. But everybody was concentrating on making sure it did not look as if they were having too much fun.
A black-tie dinner for heads of state and 800 grandees had been planned by the White House for Saturday night. It was downgraded into a less formal lounge-suit event, and an expected performance by Barbra Streisand was cancelled because it was felt to be inappropriate. The exuberant flag- waving commemoration ceremony was slashed from five hours to less than two. "Champagne is definitely off the menu," one organiser said.
This was all slightly unfortunate for the companies which had given $250,000 each to become members of the board of the Nato Anniversary Summit Host Committee. More than pounds 8m was raised in corporate sponsorship for the Washington event. Ford, Microsoft and Motorola were among the most generous donors, earning a place on the board. Dozens more organisations gave money or gifts in kind - Mercedes cars from one company to drive delegates around, bottles of gin for the parties from another.
But donors had hoped to be associated with one of the most glamorous events of the year. They thought they would have access to lobby the heads of 40 states. In fact, the Kosovo crisis meant that the tone of the event changed drastically at the last minute. Only one mobile phone company bothered to set up an exhibition stand in the conference centre. The others were worried that commercial activity would look tasteless against the backdrop of ethnic cleansing.
"The summit is not exactly celebratory any more," one member of the host committee said. "It's no longer the ideal corporate sponsorship event."