DOHA, May 25 (Reuters) - Top liquefied natural gas (LNG) exporter Qatar expects exports from its Golden Pass joint venture in Texas to begin in 2021, an advisor to the government said on Wednesday.

Staterun Qatar Petroleum (QP) owns a 70 percent stake in an LNG receiving terminal in Texas that is backed by Exxon Mobil and ConocoPhillips.

With prices down and competition increasing, Qatar is looking to diversify its energy business.

Golden Pass is seeking U.S. government approval to repurpose the facility so that it can export 15.6 million tons of U.S. gas per year.

"We already got the licence...If everything goes right by 2020-2021, we will export the first cargo from Golden Pass," Abdullah al-Attiyah, a former Qatari oil minister who advises the government on energy issues, told reporters at a media briefing in Doha attended by a QP board member.

Qatar shipped 76.4 million tonnes of LNG in 2014, or 32 percent of global supply, according to the International Group of Liquefied Natural Gas Importers.

But the tiny Gulf state faces rising competition as new projects in the United States and Australia are expected to come online in the next few years.

Attiyah said the Texas venture would make Qatar a more flexible exporter by allowing it to supply its existing customers in Europe with gas from the United States.

"We will become more dynamic in the energy market," he said.

The country's finance minister said last year that Qatar planned to invest more than $35 billion in the United States over five years in sectors including technology, energy and real estate.

(Reporting by Tom Finn; editing by Andrew Torchia and Jason Neely) ((Tom.Finn@thomsonreuters.com;))