By Becky Branford BBC News

The US is spending millions of dollars upgrading a select few air bases

The money will add to an existing bill of $1.3bn for military construction in the Middle East and South Asia - primarily Iraq and Afghanistan - in the last five years.

Much of the 2006 emergency funding is earmarked for beefing up security and facilities at just a handful of large airbases in Iraq.

This has prompted some to wonder whether the US has plans to maintain a permanent military presence - something the government has repeatedly denied.

But those concerned include the US House Appropriations Committee, which has demanded a "master plan" for base construction from the Pentagon before the money can be spent.

In a 13 March report accompanying the emergency spending legislation, it said the money was "of a magnitude normally associated with permanent bases".

A week later, after top US General John Abizaid refused to rule out a long-term presence, the House of Representatives passed an amendment to the bill stating its opposition to permanent bases.

Iraqis 'stand up'

With mid-term elections looming in November, the administration in Washington is keen to cut troop numbers in Iraq dramatically.

According to President George W Bush, as Iraqi forces become ready to "stand up", coalition forces will stand down. The Americans are already thought to have handed over at least 34 of the 110 bases it held in Iraq a year ago.

US military officials confirmed to the BBC News website that this will mean upgrading and reinforcing a handful of huge airbases into which it is planned US forces will eventually pull back, to offer quick-response air support to Iraqi ground forces.

US SPENDING ON BASES Balad base: $228.7m (2005); requested $17.8m (2006) Al-Asad base: 2005 spending unknown; requested $46.3m (2006) Tallil base: $10.8m (2005); requested $110.3m (2006)

This will allow a significant proportion of the 138,000 US soldiers in Iraq to go home, but tens of thousands will remain to staff these bases - at least in the short term.

The officials refused to confirm which bases they have in mind, but three key US airbases in Iraq are regularly cited as likely candidates.

They are at Balad, north of Baghdad, al-Asad in the western Anbar province, and Tallil, in the south. All three are in line to receive substantial chunks of the 2006 emergency budget.

Recreating small town America

The scale of the bases and the range of facilities offered to service personnel are impressive.

Some 25,000 US military and civilian personnel are stationed at the Balad base, which boasts its own neighbourhoods and airline.

At about 7km by 5km (four-and-a-half miles by three miles), the al-Asad base is so big two bus routes are needed.

Oliver Poole, correspondent for the UK's Daily Telegraph newspaper, last visited the base in January.

"In many ways they've tried to recreate the set-up of a modern US suburban town, but obviously within the context that it's a military base within the deserts of western Iraq," he told the BBC News website.

A visit to al-Asad air base

Mr Poole says there appeared to have been substantial building work at the base since his previous visit in mid-2005.

"It gave the impression of being much more permanent. I'm not saying it necessarily is permanent, but it felt less transitional."

Mr Poole quotes servicemen as saying they expect the base to remain in American hands for at least a decade, but he suggests that this is their assumption based on the challenges of quelling the insurgency in the surrounding region.

Permanent?

Some observers have interpreted the lavish funds being spent on upgrading a number of air bases as a signal that the US is anything but eager to vacate the country completely.

"What we know is that... there has consistently been money in the budget for the building of those bases," Marina Ottaway, a Middle East expert at the Carnegie Endowment for International Peace, told the BBC News website.

"One interpretation is that the [US] administration - despite the difficult political situation - has still not given up the possibility of maintaining permanent bases.

"In other words, [US Defence Secretary Donald] Rumsfeld has never given up the possibility of moving bases further east, which was part of the [reasoning behind] invading Iraq.

"I think the administration is at the very least keeping its options open."

Iraqis are also suspicious. According to a recent poll, 80% believe the US intends to retain a permanent presence in Iraq, regardless of whether the Iraqi government asked the US to leave.

'Not true'

President Bush himself recently admitted US troops would probably be in Iraq when his successor takes office in early 2009, but the notion of a permanent presence is regularly rebuffed by the US government. In February, Mr Rumsfeld insisted it was "certainly not true".

CentCom's planning director, Brigadier General Mark Kimmitt, has said the building of permanent bases would not be in the US interest.

These [bases] are more trouble than they're worth Josh Kucera Reporter, Jane's Defence Weekly

"We must continue to show that we will not become a permanent force of occupation... because we need to operate in that region in an environment of consent," Jane's Defence Weekly quoted him as saying.

Some analysts point out that the US can already count on being hosted by ally states such as Qatar, Bahrain and Kuwait.

And for Josh Kucera, Jane's Defence Weekly reporter, the US has come to realise that maintaining a presence in Iraq could be more politically costly than strategically expedient.

"The US has problems with these bases all over - look at Japan, look at the Philippines. These places are more trouble than they're worth," he says.

He points out the US has changed its defence strategy since 9/11, moving away from large, permanent overseas bases, like those in Germany and Japan, and replacing them with small bases which are not always manned.

US 'rethink'

It is likely that some US policymakers did initially think it would be useful to have a military foothold in Iraq when they were planning the invasion, says the BBC's Adam Brookes at the Pentagon.

But he says the difficulties faced there by the occupying powers may have prompted a rethink.

Much rests on the completion of a Status of Forces Agreement, accords which regulate the terms and conditions of US forces in foreign nations and are likely to be agreed when a full Iraqi government is in power.