By JONATHAN KARL

Defense officials aren't calling it a surge, but it sure looks like one.  The Pentagon is poised to send more than 3,000 additional troops to Afghanistan -- all of them Marines,  ABC News has learned.

The plan is a sign that things are not going well in Afghanistan. Commanders say they simply do not have enough troops to deal with the increased threat. 

"We are outmanned, across the board," one senior official told ABC News.

There are currently 26,000 U.S. troops in Afghanistan, the largest number since the start of the war. 

The move to send additional combat forces is in response to request by General Dan McNeill, the top U.S. commander in Afghanistan and has been approved by Joint Chiefs Chairman Admiral Mike Mullen and CENTCOM Commander Admiral William Fallon.  Defense officials say the plan will go before Defense Secretary Robert Gates for final approval on Friday. 

The Marines will move out quickly.  The plan is to get them on the ground and in the fight by April -- in time to respond to an expected spring offensive by the Taliban.

The additional forces include a Marine expeditionary unit and Marine battalion -- a total of 3,200 additional troops.  The units will include helicopters, combat forces, and trainers to work with the Afghan army.  They will go to Helmand province, a Taliban stronghold where coalition forces have been engaged in heavy combat.

Military officials say there has been a 40 percent increase in overall attacks in Afghanistan since last year and a 20 percent increase in suicide bombings. 

Defense officials tell ABC News that General McNeill has said he needs a total of 7,500 additional troops in Afghanistan.  But with the military stretched thin in Iraq, this is all he can expect to get for now, they said.