RUSSIANS ENTER KOSOVO EARLY BUT MOSCOW CALLS IT A MISTAKE; BRITISH LEAD NATO'S VANGUARD
Russian troops, despite Moscow's promises, enter Kosovo and capital city Pristina in early morning, hours ahead of NATO peacekeepers; Russians are greeted with wild celebration by local Serbs in Pristina and continue on to suburb of Kosovo Polje; Russian Foreign Min Igor S Ivanov says movement of troops was colossal mistake and that soldiers will be ordered to leave; Clinton Administration holds emergency meeting in Washington to assess situation; map; photo (M)
