By Kay Johnson

TACTICAL BASE GAMBERI, Afghanistan (Reuters) - U.S. Army Major Eric Lightfoot, serving at a remote outpost in eastern Afghanistan, knows NATO has its work cut out to prepare local forces to go it alone against Taliban insurgents once its training mission ends in two years' time.

Afghan President Ashraf Ghani said at the weekend the United States, which provides the bulk of a scaled-down force of 13,000 foreign troops tasked with training local soldiers and police, might want to "re-examine" its deadline to withdraw by the end of 2016.

His remarks came days after NATO's 13-year combat mission concluded, leaving Afghan security forces to lead the war on Taliban militants who are determined to overthrow the government and re-impose strict Islamic law.

Lightfoot spends most days at this dusty base surrounded by mountains in Laghman province planning with Afghan army counterparts how they should use D-30 artillery, heavy weapons that should give the army a hefty advantage over insurgents.

Up until a few months ago, though, the Afghans weren't using the 122-mm long-range weapon as intended – to hit targets several kilometers away, too far to be seen by those firing.

"They've been using it sort of like a tank, for direct fire at enemies they could see," said Lightfoot, who has been helping Afghans to use the complex system of spotting and grids needed to hit targets further away.

"They're getting better. They are having more successes," Lightfoot added, citing the use of Afghan artillery in recent fierce combat in Kunar province near the eastern border with Pakistan, where army and police are fighting Taliban-linked militants.

TOUGH CHOICES

But the reduced NATO mission requires painful choices.

Lightfoot said Afghan forces recently requested U.S. air support in Kunar, saying the army and police were taking heavy casualties from insurgents in a position where the Afghan artillery could not reach.

The United States refused the request, and Lightfoot advised the commanders to move the D-30 to another position where they could target the enemy.

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"They are having to get used to standing on their own," he said. "Come back in a few months, and we'll see where they are."

The number of NATO troops in the International Security Assistance Force in Afghanistan peaked at more than 130,000 in 2011 before a gradual drawdown began the following year.

According to ISAF, there were around 58,000 troops at the start of 2014 compared with some 13,000 now largely engaged in training.

The United States retains a counter-terrorism force that hunts al Qaeda and other militant targets, along with its unmanned drone strikes and limited close air support for Afghan troops under guidelines issued by President Barack Obama allowing limited combat in 2015.

Mostly, though, the new mission named "Resolute Support" is tasked with training, including the painstaking process of building up systems like logistics, supply chains, planning and strategy for Afghan forces.

That marks a major change for Lightfoot and the few hundred U.S. and about 50 Polish soldiers at Tactical Base Gamberi in Laghman province, NATO headquarters for eastern Afghanistan, for whom the new mission has an odd feeling of a war without combat.

"WHY ARE YOU STILL THERE?"

The base's hulking MRAP mine-resistant vehicles, each costing about $1 million, sit mostly idle. Troops here now never patrol "outside the wire".

"That's just not our job anymore." said Captain Jarrod Morris, the camp's public affairs officer.

Just a few months ago, Lieutenant Joshua Mathews was fighting Taliban insurgents with his infantry unit doing joint patrols with Afghan soldiers while he was based in Logar province, south of the capital, Kabul.

Now stationed at Gamberi, his new job is to provide security for U.S. military advisers. The closest thing he sees to battle is his colleague shooting animated enemies in a video game on the large-screen television above their office desks.

While foreign soldiers are limiting exposure to battle, they remain targets. Even in Kabul, NATO forces typically fly by helicopter over the 5-10 km from the coalition headquarters to the capital’s military airport because of the threat of suicide bombers on the roads.

Afghanistan's own security personnel are dying at a rate of about 100 per week, a level the U.S. military has described as unsustainable, and foreign forces are advising them on how to reduce the rising casualty rate.

By comparison, about 3,500 foreign soldiers have died in the Afghan war since 2001, including around 2,200 Americans.

At Gamberi, there is more training and talking than fighting. The base's "fire line" hasn't shot its giant 155-mm Howitzer artillery in anger for months.

"Last time I talked to my mom, she said 'The war is over. Why are you still there?'" said Specialist James Dye.

(Editing by Mike Collett-White)