UPDATE 2-UK's newest LNG terminal to get first cargo Tues

* BG Group tanker heads to new Welsh terminal

* Number of commissioning cargoes needed unclear

(Recasts, adds operator confirmation, U.S.-bound cargo)

By Daniel Fineren

LONDON, July 10 (Reuters) - Britain's newest liquefied natural gas terminal, Dragon LNG, is expected to take delivery of its first cargo of super-cooled gas on Tuesday, a spokeswoman for the plant in south Wales said.

"The first commissioning cargo is expected imminently and currently scheduled for July 14," the spokeswoman said on Friday. She declined to say how many more commissioning cargoes would be needed to prepare the terminal for full commercial operations.

The local port authority website says BG Group's (BG.L) Methane Lydon Volney, which can carry 145,127 cubic metres of LNG, is to arrive on Tuesday morning. AISLive ship tracking data showed it was off the coast of Portugal on Friday.

Dragon LNG, which had been due to start up in 2008, is a joint venture in which BG holds a 50 percent stake, Malaysia's Petronas [PETR.UL] 30 percent and Dutch 4Gas 20 percent.