* Iraq main northern oil export line shut for 40 days
* Officials blamed Islamist bombers with Syrian links
* Attacks on repair crews threaten hopes of resumption
MOSUL/BAGHDAD, April 10 (Reuters) - Militants whose bombs have shut Iraq's main northern oil export pipeline for 40 days are preventing repairs, threatening to extend an outage that is already the longest since the days of sanctions in the 1990s.
Targeting the Kirkuk-Ceyhan pipeline where it crosses a stretch of desert known as Ain al-Jahash, or Donkey Springs, the saboteurs - described as Islamists by Iraqi officials - have set several more bombs since a first blast halted oil on March 2.
Significantly for an Iraqi government hoping for a big rise in exports this year - and long used to brief halts on the route to the Mediterranean - gunmen have also massacred repair crews, prompting oil executives in Mosul to question optimism in Baghdad that the pipeline should be back in action next week.
"We have decided to stop all repair operations in Ain al-Jahash until we are sure our crews won't get killed," a senior official of Iraq's North Oil Company told Reuters. "Oil flow is important, but the blood of our employees is more precious."
Oil Minister Abdul Kareem Luaibi said this week that pumping to Turkey's Ceyhan port should resume next week after repairs to a line that carries about a fifth of Iraq's total crude exports.
But managers at the NOC and security officials in Mosul - none of whom would speak publicly - said it would take much greater force to ensure the pipeline's security in area where al Qaeda-linked groups have expanded their operations from Syria.
"It's impossible for us to control it fully," said a senior security official said of Ain al-Jahash, which NOC staff have nicknamed "Tora Bora" after al Qaeda's Afghan bastion. "It'll take a whole army, with tanks and jets, to hold the ground."
Two security officials in Mosul said a "clean-up" operation against militants south of the city was being prepared to protect the pipeline but the timing was unclear: "We have to find a solution to the deteriorating security in southern Mosul quickly, or else things will get out of control," one said.
Maintenance crews have threatened to walk out rather than be sent to the area, where five technicians were gunned down a month ago before they could repair the damage caused by the first blast. Since then, three more bombings have inflicted further damage on the line. Three further repair missions have been thwarted by ambushes, despite having military escorts.
NOC officials blame the Islamic State in Iraq and the Levant (ISIL), a Sunni Islamist group previously linked to al Qaeda which is fighting Syria's Iranian-backed administration and also operating over the border against Iraq's Shi'ite-led government.
The militants have benefited from support among Sunnis in Iraq's northwestern desert, who resent both the Shi'ites brought to power in Baghdad by the U.S. overthrow of Sunni Saddam Hussein in 2003 and also of the autonomous Kurds to their east.
Several local officials in Mosul said efforts had been made to co-opt residents of villages in the area to help the authorities by offering jobs in public services and security forces. But most refused, fearing reprisals from insurgents.
"If we join the government forces then who will protect us?" asked Anwar al-Hadidi, a 27-year-old farmer who travelled to Mosul from Ain al-Jahash to work as day labourer. "Al Qaeda would slaughter us immediately. If the security forces can't protect a metal pipe, then how will they save our lives?"
During the U.S. invasion, the Kirkuk-Ceyhan line was shut for 25 days, officials said. Damaged by Western bombing in the 1990 Gulf War and then kept closed by U.N. sanctions imposed on Saddam, it reopened in 1996 when some oil exports were allowed.
Occasional attacks in the past decade have been repaired more quickly. But the latest sabotage has forced the NOC to shut down some production stations in two major oilfields at Kirkuk, squeezing total production to around 225,000 barrels per day (bpd) from around 550,000 bpd before the attack, officials said.
Militants have also attacked energy facilities near Mosul, away from the pipeline. In late March, gunmen managed to plant four bombs inside the Qayara oilfield to the south of the city and bombs went off near an oil well. It is still leaking gas.
Prime Minister Nuri al-Maliki replaced army commanders in Mosul last month over the failure to secure the areas around the pipeline and curb the growing power of the ISIL.
The bulk of Iraq's oil is produced in the south and shipped abroad through the Gulf but the closure of the northern route has held back a hoped-for growth in exports that have also been hampered in the north by disputes with the Kurdish authorities.
Iraq, the second biggest oil producer in OPEC, has been the world's fastest growing oil exporter following long years of isolation and violence and many in the global industry expect sales to increase significantly this year following a drop-off in the momentum of export growth in 2013.
An average of around 300,000 bpd was pumped through the Kirkuk-Ceyhan line last year. Luaibi said on Wednesday he hoped Iraq would be sending 1 million bpd by the end of the year with the help of a new 200-km pipeline to Turkey.
Officials in Turkey complained that they had been kept in the dark by their Iraqi counterparts about the state of the pipeline, and did not know when exports would resume: "Turkish and foreign companies are unhappy with this situation because they can not buy oil," a senior Turkish energy official said.
"We keep asking but all they say is we should wait".
(Additional reporting by Mustafa Mahmoud in Kirkuk and Orhan Coskun in Ankara; Editing by Isabel Coles and Alastair Macdonald)