* Well had leaked for over 2 months

* Montera oilfield flagship of Thai PTTEP

(Recasts lead and adds detail, background)

By Michael Perry

SYDNEY, Nov 3 (Reuters) - Thailand's PTT Exploration and Production (PTTEP) <PTTE.BK> has plugged an oil well in the Timor Sea that had leaked for over 2 months, creating what environmentalists said was one of Australia's worst ever spills.

PTTEP, part of the Thai state-controlled energy group PTT <PTT.BK>, said in a statement on Tuesday it had "killed the leaking well and stopped the main fire at the Montara well head platform and surrounding the West Atlas drilling rig".

"Some material on the topside of the West Atlas rig might still be on fire but it is expected to be extinguished as the fuel source burns out," PTTEP's Australasia unit said.

A picture issued by PTTEP of the rig, owned by Norwegian driller Seadrill <SDRL.OL>, showed light black smoke rising from a charred and badly damaged structure.

The rig, worth around $200 million dollars according to analysts at Citigroup, caught fire on Sunday during operations to stop the leak.

Between 300 and 400 barrels a day were estimated to have been leaking from the well, the Department of Resources and Energy and Tourism said on its website, and environmentalists had warned that birds and endangered sea life were at risk.

PTTEP said it plugged the leak by pumping 3,400 barrels of heavy mud down a relief well.

The West Atlas rig was due to start commercial operations this month. The Montara field could be one of the main sources of profit for PTTEP in the second half of this year as analysts expect higher output from new oil and gas fields to boost its sales.

PTTEP plans to produce about 35,000 barrels per day of oil from Montara, which should boost its 2009 sales to 240,000 bpd.

Montara is the flagship in the exploration and production business for PTTEP, which is involved in about 40 oil and gas exploration and development projects in 14 countries in the Middle East, Africa and Asia.

Citigroup noted that Seadrill had physical damage insurance and "loss of hire" insurance in place, which could limit any financial impact on the company from the incident. (Additional reporting by Tom Bergin in London)

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