* Pays equivalent of around $7.8 bln
* Sign of Guards' growing influence under Ahmadinejad
* Agency says biggest trading of shares ever on Iran exchange
* Force involved in oil, defence, transport and construction
* Foreign investors wary of Iran due nuclear dispute (Adds detail, background)
By Hashem Kalantari
TEHRAN, Sept 27 (Reuters) - A consortium affiliated to the elite Revolutionary Guards bought 50 percent plus one share in Iran's state telecommunications company for the equivalent of around $7.8 billion, Iranian media reported on Sunday.
The move was a further sign of the Guards' growing influence in Iran since hardline President Mahmoud Ahmadinejad, himself a former Guardsman, came to power in 2005.
Revolutionary Guards played a key role in quelling street unrest that erupted after Ahmadinejad's disputed re-election in June.
The semi-official Mehr News Agency, citing an official of Iran's Privatisation Organisation, said it was the biggest trading of shares ever on the Islamic Republic's stock exchange.
It said two Iranian consortiums had been competing for the controlling stake in Telecommunication Company of Iran (TCI) and Etemad Mobin won. A third Iranian bidder was disqualified for security considerations, ISNA news agency reported.
The official IRNA news agency said Etemad Mobin belongs to the cooperative foundation of the Guards, a force that was formed after Iran's 1979 Islamic revolution.
Mehdi Aghdaie, deputy director of the Privatisation Organisation, said the value of the sold TCI stake amounted to around 10 percent of the stock market's total capitalisation.
Iran's economy is dominated by the state but the government has been seeking to speed up privatisations after the constitution was changed to encourage the sale of assets.
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The then head of the Tehran Stock Exchange last year told Reuters several foreign firms were showing interest in buying a major stake in TCI.
But with foreign investors increasingly wary of Iran because of its nuclear row with the West, some analysts say assets to be sold off may simply end up being transferred within its vast public sector.
Iran, the world's fifth-largest oil exporter, is under U.N. and U.S. sanctions for refusing to halt sensitive nuclear work.
Shares representing 5 percent of TCI fetched $360 million when they were sold on the stock exchange last year, stock exchange officials have said.
The gradual sale of TCI, which provides all of Iran's landlines, is part of a wider drive to speed up the sale of state-owned companies, though not in the upstream oil and gas industry which will remain in government hands.
South Africa's MTN Group, sub-Saharan Africa's biggest mobile operator, is present in Iran via a 49 percent stake in Irancell, a mobile phone company competing with TCI.
The Revolutionary Guards became heavily involved in reconstruction after the 1980 to 1988 Iran-Iraq war and has expanded its work to cover areas such as import-export, oil and gas, defence, transport and construction.
The Corps has become a major contractor, with ties to firms controlling billions of dollars in business, construction, finance and commerce, the U.S. Treasury has said.
A RAND Corporation report this year said Khatam al-Anbia, an engineering firm affiliated to the Guards, had been awarded more than 750 contracts in construction, infrastructure and energy.
Last year, the International Monetary Fund said Iran's divestment process had gathered pace, but "given the lack of large private investors, many government-owned entities were acquired through non-cash or deferred settlements by quasi-public sector institutions." (Additional reporting by Hossein Jaseb; Writing by Fredrik Dahl; Editing by David Holmes)