Defense Secretary Robert Gates has decided to send an additional 1,400 Marine combat forces to Afghanistan, officials said, in a surprise move ahead of the spring fighting season to try to cement tentative security gains before White House-mandated troop reductions begin in July.

The Marine battalion could start arriving on the ground as early as mid-January. The forces would mostly be deployed in the south, around Kandahar, where the U.S. has concentrated troops over the past several months…

Commanders are examining other proposals to temporarily boost the number of combat troops in Afghanistan in addition to the Marines authorized Wednesday. If the plans are approved, the front-line fighting force could be increased in total by as many as 3,000 troops.

U.S. commanders in Afghanistan face intense pressure to show sustainable security gains in the first half of 2011. Military officials fear an upswing in attacks by the Taliban in the spring could convince the White House that the Pentagon’s war strategy is flawed and that the troop pullout—the details of which have yet to be ironed out—should be accelerated.