* Global capacity down just 0.6 percent to 2.36 bln T - OECD
* Excess capacity still nearly double what is needed
* 40 mln T capacity additions underway for 2017/19
* New capacity undermines cuts in China, threatens prices
LONDON, Oct 10 (Reuters) - The global steel sector's recovery from a glut-fueled slump, driven by Chinese capacity cuts, is being put at risk by surplus capacity being built in the Middle East and Asia, sources and experts say.
Figures from China show it has cut nearly 100 million tonnes of legal steel capacity and 120 million tonnes of illegal low-grade capacity since last January, but industry analysis shows only marginal declines in overall capacity.
According to the latest estimate from the Organisation for Economic Cooperation and Development (OECD), global steel-making capacity stood at 2.36 billion tonnes in the first half of 2017, easing just 0.6 percent from 2.37 billion in 2016.
The figures are evolving and may not yet reflect the full extent of capacity reductions taking place, a source close to the OECD Steel Committee, which produced the estimates, said. But he also said the overall global overcapacity picture was worrisome.
"Excess capacity remains at alarmingly high levels," OECD Steel Committee chair Lieven Top said late last month, following the release of the estimates at its bi-annual meeting.
According to the OECD steel capacity report on which the estimates were based, some 23 million tonnes of potential output additions are underway in the Middle East, primarily Iran. These should come on stream during 2017-2019, with another 7 million tonnes planned for possible start-up during the period.
The extra capacity is headed in part for the export market given that the World Steel Association (worldsteel) estimates demand in the Middle East will grow by a total of just 3.7 million tonnes this year and next.
Iran, which became a net steel exporter for the first time last year, says it aims to export 20-25 million tonnes of steel annually by 2025, equivalent to almost a third the amount of steel China is set to export this year.
"Frankly, any region that increases capacity poses a distinct risk to future steel pricing and profit," Alistair Ramsay, research director at Metal Bulletin Research, said.
Experts say that to meet demand and sustain profits, the steel industry requires at most 400 million tonnes of spare capacity over and above the current 1.63 billion tonnes it produces each year. But with global production potential at 2.36 billion, the industry has some 730 million tonnes spare.
Despite this, the OECD report shows a total of nearly 40 million tonnes of capacity additions are underway and could come on stream in 2017-19, including the Middle East additions, and some additions in Asia.
The report also shows another 54.5 million tonnes of capacity is planned for possible start-up during the period, primarily in Asia, with some in the Middle East, Africa, Russia and Ukraine.
The numbers are gross estimates that do not take into account capacity cuts going forward, the OECD source said, but they still sound a note of caution for further investment.
"We do not expect sufficient global demand growth to justify the extent of capacity additions cited (in the OECD report). However, certain individual investments can still make sense, if very low cost or where they are best placed to serve local markets," CRU analyst Chris Houlden said.
Global steel prices have soared 50 percent since Jan 1, 2016, according to data from consultants MEPS.
Share prices of steel companies jumped 70 percent during the period, according to the Thomson Reuters Global Steel Index, with the sector seeing some high profile acquisitions like ArcelorMittal's 1.8 billion euro ($2.1 billion) offer for Italy's Ilva, Europe's largest and most troubled steel plant.
CHINA BLAME GAME
Price rises have been driven by the Chinese capacity cuts, but these should wane going forward. The China Iron and Steel Association said the country had essentially completed its five-year target, set last year, to cut 100-150 million tonnes of excess capacity.
Much of the blame for the global steel sector crisis of 2015 has been directed at China - producer of half the world's steel - with 121 duties in place globally on Chinese output as of end-June this year, a U.S. Department of Commerce report showed.
In the United States, President Donald Trump has repeatedly threatened to take a tough line on what he says is unfairly traded Chinese steel, even launching an investigation into whether steel imports pose a risk to U.S. national security.
"Politicians in the West and western steel producers love to blame China for overcapacity, which is fair to an extent; but Chinese mills have shouldered most of the burden of capacity reductions in the last two years, Roger Bell, director of mining research at Hannam and Partners, said.
(Additional reporting by Mai Nguyen in Hanoi; Editing by Veronica Brown and Jane Merriman)