The European Union has agreed in principle to take over NATO's Bosnia peacekeeping mission in mid-2004.
A senior diplomat said Britain would be in command of the force which would comprise of some 6,000 soldiers.
The EU's fledgling rapid reaction force made its debut in peacekeeping operations in April, sending a tiny force to the former Yugoslav republic of Macedonia, and followed up with a mission in the Democratic Republic of Congo.
The Macedonia mission was seen as a model for burden-sharing with Washington in which the EU would take more responsibility for stabilising and rebuilding the Balkans after a decade of ethnic wars was halted by US-led military intervention.
NATO is expected to review its forces in the western Balkansthis autumn, setting targets for 2004. Diplomats say it islikely to reduce its force in Bosnia to around 6,000-8,000 from13,000.
The US-dominated alliance would still have a role inBosnia if the EU took over, providing the bloc with planning andlogistical support as it does for the Macedonia operation.
Officials said there was no formal decision because it wasan informal meeting, and NATO nations would have to be consultedat a defence ministers' conference next week.