* 2012 output seen at low end of target range
* Repairs made to oil sands plant in early Nov.
* Shares down C$0.10 at C$32.58 in Toronto
CALGARY, Alberta, Dec 6 (Reuters) - Unplanned maintenance at Suncor Energy Inc's oil sands operation has pushed production to the low end of its forecast range for the year despite the startup of a new production unit, Canada's largest energy company said on Thursday.
Suncor said average oil sands output in 2012 is now expected to be closer to 325,000 barrels per day than 340,000 bpd due to unplanned repairs at the company's base plant in northern Alberta in early November. In October, it had trimmed the upper end of its forecast.
In 2011, its oil sands production averaged 326,500 bpd.
Production in November averaged 318,000 bpd, down 18,000 bpd from the previous month, the company said.
However, the repairs to the oil sands plant are complete and the operation pumped 380,000 bpd at the end of November, it said.
Earlier this week, Suncor said it expected oil sands production to increase 12 percent and overall oil and gas output 8 percent in 2013. Capital spending is pegged at C$7.3 billion.
Chief Executive Steve Williams has signaled that Suncor will not be rushing into major capital projects to boost production at any cost.
The company has pushed back plans to construct the Fort Hills oil sands project, and said on Monday it and partner Total SA will decide by the end of the first quarter whether to go ahead with a multibllion-dollar upgrading plant known as Voyageur.
Williams has already said the proposed facility's economics are threatened by surging volumes of light shale oil in regions such as the North Dakota Bakken.
It has started producing bitumen at the fourth stage of its Firebag steam-driven oil sands project, the company said, pushing overall volumes to 130,000 bpd.
Suncor shares were down 10 Canadian cents at C$32.58 on the Toronto Stock Exchange, close to the level when Williams took the helm from retired CEO Rick George at the start of April.
The company also said on Thursday that the floating production vessel at the Terra Nova oil project, off the coast of Newfoundland, was in the final stages of lengthy maintenance and that output from the field should return to full rates by the end of the year.