But Britain's overall deployment in Afghanistan will only increase by 300 since the military also will reduce its manpower in Kabul, the capital, by 500, he said.
To prepare for that, the United States is donating equipment and weapons to the Afghan army to improve its ability to defend the country on its own and to one day allow U.S. and NATO -led forces to pull back.
Browne said Britain's military commitment to southern Afghanistan will be increased by about 800 troops by the end of this summer, bringing the total British deployment in Helmand province to 5,800. British soldiers have faced fierce resistance from Taliban militia in Helmand, where most of Britain's 46 fatalities in Afghanistan have occurred.
Britain's military presence in Kabul, meanwhile, will be reduced by about 500 personnel as Britain hands over command of the NATO-led International Security Assistance Force to the United States this weekend, Browne said in a written statement to lawmakers.
The result of the two changes will be an increase of about 300 in the overall British commitment to the country.
British Harrier GR7 and GR9 jets, Apache attack helicopters, Viking all-terrain vehicles and Royal Engineer support units now in Helmand will remain there until April 2009, he said.
Browne's announcement follows arguments within NATO over which countries will supply troops to meet a shortfall identified by commanders on the ground in southern Afghanistan.
Last month, former NATO Secretary General Lord Carrington accused France and Germany of "not pulling their weight" by providing troops for front-line duties in the south, where Taliban maintain control over large areas.
He warned that Afghanistan could sound "the death knell" for the alliance.