* Iron ore to average $115 by 2015 vs $126 in 2012
* China iron ore imports, crude steel output growth to slow
* With profits at stake, miners may go slow on mega projects
(Adds Baosteel, Blackrock outlook and graphic)
SINGAPORE, Oct 30 (Reuters) - Iron ore prices may drop nearly 10 percent over the next three years as top consumer China's economic growth shifts to a slower gear, threatening to squeeze profits at global miners Vale, Rio Tinto and BHP Billiton, a Reuters poll showed.
Closely tied to the fate of the steel-intensive Chinese economy, iron ore prices and China's gross domestic product growth both hit three-year lows this year. Beijing's shift to a more balanced growth model after a decade of investment-driven expansion could curb the increase in steel demand.
Iron ore is forecast to average $120 per tonne in 2013, down from an estimated $126 this year as China's crude steel production growth weakens, according to the median estimate in a Reuters survey of 12 analysts.
The price average should slip further to $119 by 2014 and to $115 by 2015, the poll showed.
``China continues a structural shift away from fixed asset investment-led growth, which means steel demand growth will remain below GDP growth rates in the future,'' said Ian Roper, commodities strategist at CLSA.
The most bearish among those polled, CLSA's Roper expects iron ore prices to average $85 and $75 in 2014 and 2015, respectively.
``Most forecasters are still in blind bullish mode thinking Chinese steel demand will grow and grow (strongly) forever,'' he said.
The new norm for China's GDP growth is likely to be 7-8 percent, economists say, as Beijing seeks sustainable expansion after years of double-digit rises. For 2012, the world's No. 2 economy is forecast to grow 7.7 percent, the slowest pace since 1999.
A slowdown in the Chinese economy -- which grew by 7.4 percent in the third quarter, the weakest since January-March 2009 -- dragged down iron ore prices in September to below $87 per tonne, their weakest in about three years.
Slower steel demand had forced Chinese producers to limit their iron ore stockpiles, prompting top miners to review expansion plans that were pinned on hopes Beijing will continue to suck in all the raw material they produce.
China's iron ore imports are forecast to grow 6 percent to 774 million tonnes in 2013 from a projected 730 million tonnes this year, the poll showed, slowing from last year's 10.9 percent increase. Annual import growth is seen falling to less than 5 percent in 2015.
Crude steel production may rise 3.5 percent to 735 million tonnes from a predicted 710 million tonnes in 2012, according to the poll. In 2011, output grew 8.9 percent, and by 2015, the annual increase is seen dwindling to 2.6 percent.
Baoshan Iron and Steel Co Ltd, China's biggest listed steelmaker, sees the business environment as difficult for several years.
``Judging from current global and domestic economic growth, it is realistic to expect the 'cold winter season' to last for 3-5 years, and the steel sector will not be an exception,'' Ma Guoqiang, general manager at Baosteel, told an online briefing.
Even with iron ore prices unlikely to return to record levels of near $200 per tonne reached last year, the big margins enjoyed by low-cost producers Vale, Rio Tinto and BHP Billiton mean they are going ahead with plans to boost output.
``The current pricing is enough to incentivise them to lift their output. Prices being where they are will probably slow the urgency of the capital spending, but even so there should be a desire to get more production into the market,'' said Graeme Train, Macquarie commodity analyst in Shanghai.
The major miners spend around $40 or less to produce a tonne of iron ore, keeping their margins high even with prices down more than 37 percent down from all-time peaks.
``The share prices today, we believe, are factoring in a pessimistic outlook, one in which commodity prices are going to average lower than what we see today,'' Catherine Raw, co-manager of BlackRock Inc's BGF World Mining Fund, told reporters in Sydney on Tuesday.
``From our point of view, this creates a huge amount of value and a huge amount of opportunity.''
BlackRock, the world's largest money manager, was overweight in iron ore companies including Rio Tinto and BHP Billiton and sees a long-term price of around $120 a tonne.
But with low-cost producers dominating the market, slower demand growth from China suggests the global seaborne iron ore market may be in surplus from next year, a year earlier than the previously estimated.
While medium-term production plans may be untouched, miners are less gung-ho longer term. With profits likely to be much less than in recent years, cost cuts have become a must.
Brazil's Vale, the world's top iron ore supplier, has put on hold its $5 billion Simandou iron ore venture in Guinea after its third-quarter profit slid 66 percent and is looking to sell underperforming assets to curb costs.
Miners will be ``increasingly cautious about introducing mega-projects, of the scale that could disturb the pricing equilibrium,'' Hatch Consulting said.
(Additional reporting by Silvia Antonioli in LONDON, David Stanway in BEIJING and Ruby Lian in SHANGHAI; Editing by Ed Davies and Simon Webb)