UPDATE 1-Noble ups bid to $429 million for Gloucester Coal

* Noble ups Gloucester offer about 17 pct to $429 million * Offer hinges on Gloucester dropping Whitehaven bid (Adds details of offer, share prices)

SYDNEY, May 15 (Reuters) - Commodity trader Noble Group (NOBG.SI) raised its offer for Australian miner Gloucester Coal Ltd (GCL.AX) by 17 percent to A$572 million ($429 million), as it seeks to foil a plan by Gloucester to acquire another coal company.

Hong Kong-based Noble upped its offer to A$7 a share from the A$6 a share it had bid previously for the 78.3 percent it did not already own in Gloucester.

Noble said its latest offer was conditional on a reverse-takeover by Gloucester of Whitehaven Coal Ltd (WHC.AX) not proceeding.

Gloucester is proposing a merger with Whitehaven via a scrip-based reverse takeover, which has an implied value of A$4.83 per share.

Shares in Gloucester, which produces power station coal and coking coal used by steelmakers, rose 1.55 percent to A$5.89 on Friday.

Noble's announcement of its new offer came after the market closed.

Noble, which buys about 25 percent of Gloucester's coal output, closed down 3.29 percent at S$1.47 a share. (Reporting by James Regan; Editing by Nathan Layne)