WASHINGTON — Engineers are working furiously to prepare for a surge of troops and supplies into Afghanistan to carry out President Barack Obama's war plan, the top US military officer said.

"The debate is over. The decision has been made. It is time to execute," Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, told a press conference in Washington.

Hundreds of Marines would be in southern Helmand province next week, tonnes of supplies were due to be delivered and the military was "accelerating deployment plans for the rest of the extended surge forces," Mullen said.

"We're on the balls of our feet, leaning forward," he said.

The 1,500-strong Marine contingent was the first of 16,000 troops ordered to deploy in the next several months after Obama's long-awaited announcement last week of a new strategy for Afghanistan.

Army and navy engineers were focused on the monumental logistical challenge of moving 30,000 additional troops and supplies to Afghanistan, expanding airfields and remote bases, Mullen said.

"Tens of thousands of tonnes" of supplies -- including winter gear and construction materials -- were being prepared for delivery, he said.

Mullen said land-locked, mountainous Afghanistan presented a much more difficult logistical challenge than Iraq, which has a port and a large US base in neighboring Kuwait.

"We don't have for that country a major logistics hub akin to the one we have in Kuwait," he said.

"We don't have in Afghanistan anywhere near the number of runways or rail hubs or road networks that exist in Iraq."

But he said he was confident that the bulk of the 30,000 reinforcements would be in place by mid-summer next year and the remaining troops by the autumn.

Mullen's comments came after the US and NATO commander in Afghanistan, General Stanley McChrystal, told lawmakers this week he believed the larger US-led force could shift the momentum against a spreading Taliban insurgency.

At congressional hearings this week, Democrats in Obama's party expressed serious doubts about the eight-year-old war but were not expected to block funding for the troop surge, which will cost an estimated 30 billion dollars.

The buildup will include an expansion of special forces units, Mullen said, referring to the elite troops used to hunt down key insurgent leaders.

The NATO commander, McChrystal, is steeped in special operations and in Iraq his forces were credited with killing Abu Musab al-Zarqawi, leader of Al-Qaeda in Iraq.

Mullen also indicated the escalating commitment meant the US Army would have to delay plans to allow war-weary soldiers more time at home between combat tours.

The Pentagon has set a goal of increasing "dwell time" to two years at home for every year deployed and the Marine Corps will reach that goal next year.

But Mullen said the army would not meet the objective and that it would "take a couple more years to do that."

Senior commanders have struggled to ease the strain on the Army and the Marines from the wars in Iraq and Afghanistan, amid rising rates of depression, divorce and suicide believed to be fueled by repeated deployments.

The head of US Transportation Command meanwhile said on Wednesday that the buildup was complicated by the approaching winter but said the military was ready and had prepared airfields in recent months.

General Duncan McNabb said about the same number of troops were ferried to Afghanistan earlier this year in about the same time frame.

"On the positive side, we've just done that. On the more difficult side, we're talking about doing it in December," he said.

About half the Afghan mission's supplies move by land through Pakistan, a third through northern routes -- including via Russia -- and 20 percent by air, McNabb said.

The military delivers all lethal and sensitive cargo by air as a precaution, but the cost of air shipments is about 10 times more than by land, he said.

US commanders were even considering using unmanned aircraft to deliver supplies to combat troops as well, which would reduce the cost of air dropping cargo, the general added.

www.google.com/hostednews/afp/article/ALeqM5ho59mOHixeaUapNUmqtjOIYo3ByA