LONDON - British troops will begin withdrawing from Iraq in March and will mostly be gone by June, the Ministry of Defense said Wednesday.

Britain has about 4,000 troops in southern Iraq. It expects to begin withdrawing them after regional elections planned for next month, the ministry said, confirming reports in British media. The number of troops will fall to 300-400 by mid-year, the reports said.

A U.S. brigade will replace the British force at Basra airport, ministry officials told reporters from British media in a briefing Tuesday. The ministry confirmed reports of the briefing to The Associated Press.

A new U.S.-Iraqi security pact calls for 150,000 American troops to be withdrawn from Iraq in two stages by the end of 2011. Iraq's Parliament has yet to ratify a new status of forces agreement with Britain to allow British troops to stay into next year.

Prime Minister Gordon Brown said after a visit to Iraq in July that he "would expect a further fundamental change of mission in the first months of 2009, as we make the transition to a long term bilateral partnership with Iraq."

Brown has not announced a timetable.

The Times reported that the exact timing of the first troop withdrawal will depend on the arrival of an American two-star military headquarters at the airport base northwest of Basra City.

Britain had about 40,000 troops in Iraq at the height of the U.S.-led invasion in 2003, and 177 members of the armed forces and civilian defence workers have died on duty.

The most recent death was on Dec. 4, when Lance Cpl. David Wilson was killed by gunfire. It was the first combat death suffered by British forces in Iraq since March 26.

Military commanders have warned that British troops are overstretched from commitments in Iraq and Afghanistan. Air Chief Marshal Jock Stirrup, the chief of the Defense Staff, said last month that a major withdrawal of Britain's 4,000 troops in Iraq in 2009 won't mean additional forces can immediately be sent to Afghanistan.