First copper from Congo-China deal due by year end - government

* Copper output seen starting at 50,000 tonnes per year

* Congo seeks 400,000 tonnes/yr within two decades

By Aaron Ross

KINSHASA, May 21 (Reuters) - A joint venture between Democratic Republic of Congo's state miner and two Chinese companies, signed under a 2009 "minerals for infrastructure" deal, will begin producing copper before the end of 2015, Congo's government said on Thursday.

Under the deal Chinese companies pledged to build $3 billion worth of roads, railways, schools, and hospitals in return for a 68 percent stake in a joint venture operating copper plants with state miner Gecamines in the southern Katanga province.

The Chinese firms involved in the Sicomines joint venture are Sinohydro Corp and China Railway Group Limited.

The Congolese government office charged with overseeing implementation of the deal said copper output would begin "in the fall of 2015" at a rate of 50,000 tonnes per year, rising to an expected 400,000 tonnes per year over the next two decades.

"This mutually beneficial cooperation with our Chinese partners is a strong example for others interested in investment opportunities in (Congo)," Moïse Ekanga, executive secretary of the office, said in a statement.

An original $9 billion deal signed in 2007 was reduced to about $6 billion after the International Monetary Fund (IMF) objected to the amount of debt Congo was taking on.

Ekanga led a tour of the Sicomines plants taken last weekend by the IMF's resident representative in Congo, the World Bank's country director and several foreign diplomats.

Congo, which vies with Zambia to be Africa's top copper producer, extracted more than 1 million tonnes of the metal for the first time in 2014.

The mining sector helped power economic growth of 9.5 percent in 2014, according to the government. However, after two decades of armed conflict, Congo still ranks 186 out of 187 countries in the U.N. Human Development Index.

The government has predicted 10.3 percent growth for 2015. (Reporting By Aaron Ross; Editing by David Lewis and Greg Mahlich)