UPDATE 2-BP-led consortium takes on Iraq's Rumaila oilfield

* Rumaila oilfield capacity now 1.1 million bpd

* Consortium aims to raise capacity to 2.85 mln bpd

* Fee of $2 a barrel accepted vs $3.99 proposed by companies

* Contract offers "foothold" in Iraq, analysts say

(Updates with detail, comment)

BAGHDAD, June 30 (Reuters) - A consortium led by BP (BP.L) and including China National Petroleum Corp [CNPET.UL] (CNPC) on Tuesday accepted a contract to develop Iraq's biggest oilfield, the 17-billion barrel southern Rumaila field.

The original winner of the bidding for the field, an Exxon Mobil-led (XOM.N) alliance, had rejected the Iraqi Oil Ministry's maximum proposed per barrel fee for the contract, giving the BP group an opening to take it on.

The BP/CNPC alliance had to accept a fee of $2 for every barrel of additional oil produced, compared with a fee of $3.99 included in their initial offer.

"We asked each of the companies to accept and BP and CNPC accepted the ministry's figure and for that reason their bid is accepted," said Oil Minister Hussain al-Shahristani.

Rumaila is the workhorse of Iraq's oil sector, with a current capacity of 1.1 million barrels per day (bpd) out of Iraq's total national output of 2.4 million bpd.

It was one of six already producing oilfields and two undeveloped gas fields offered up on Tuesday in Iraq's first auction of major oil contracts since the 2003 U.S.-led invasion.

"FOOTHOLD"

Analysts said BP had probably been willing to accept the less favourable terms offered by the ministry because the upstream Iraqi oil industry offered a unique opportunity to tap onshore oil reserves.

Iraq has the world's third-largest proven oil reserves, estimated at 115 billion barrels, but its petroleum industry has been devastated by years of war and international sanctions.