Britain's FTSE index set to post fourth consecutive month of gains

* FTSE 100 index flat

* Set to post fourth straight month of gains

* Hits one-month high before easing

* Inmarsat (Other OTC: IMASF - news) falls ahead of FTSE reshuffle (Recasts, adds detail and quote, updates prices)

By Kit Rees and Atul Prakash

LONDON, May 31 (Reuters) - Britain's top share index was set to post its fourth straight month of gains on Tuesday, steadying despite a fall in satellite communications company Inmarsat (LSE: ISAT.L - news) ahead of a FTSE reshuffle later in the week.

The FTSE 100 index was flat in percentage terms at 6,268.66 points by 1435 GMT, outperforming the broader European market.

While losses were broad-based, with ITV (LSE: ITV.L - news) , Standard Chartered and Kingfisher (LSE: KGF.L - news) among the top fallers, shares in satellite company Inmarsat dropped 3.5 percent with analysts citing the possibility of the firm being relegated in Wednesday's FTSE 100 index reshuffle.

Inmarsat has fallen over 36 percent so far in 2016.

"Inmarsat's problem's are partly related to the sector, and partly related to the oil price. Their clients are very largely maritime, and maritime clients in turn are quite often linked to the energy sector - it's just getting off its knees," Ken Odeluga, market analyst at City Index, said.

The UK mining index also fell, down 0.3 percent as copper prices declined on a resurgent dollar following increasing expectations of a U.S (Other OTC: UBGXF - news) . interest rate hike.

Copper prices remained on track for a more than 7 percent decline in May, the biggest monthly drop since November.

St. Louis Federal Reserve President James Bullard on Monday echoed remarks by U.S. central bank chief Janet Yellen that global markets appear to be "well-prepared" for a summer interest rate hike by the Fed, although he did not specify a date for the move. A stronger dollar makes commodities more expensive for holders of other currencies.

Shares (Berlin: DI6.BE - news) in Glencore (Xetra: A1JAGV - news) , BHP Billiton (NYSE: BBL - news) , Antofagasta (Other OTC: ANFGF - news) , and Rio Tinto (LSE: RIO.L - news) fell 0.2 to 1 percent.

However, the commodity-heavy FTSE 100 index touched a one-month high of 6,290.07 points earlier in the session. It (Other OTC: ITGL - news) has remained in positive territory this month and was headed for its fourth straight month of gains.

"The FTSE 100 is still in the midst of sideways consolidation, but with a welcome test of last week's 6,280 ceiling and a close venture to 6,300," said Augustin Eden, analyst at Accendo Markets, adding that a drop towards 6,240 would send a bearish signal for the index.

Among mid-caps, Alliance Trust rose 3.3 percent after RIT Capital Partners (LSE: RCP.L - news) made an informal merger proposal for the investment firm. RIT confirmed talks saying a merger possibility was at "a very preliminary stage of consideration".

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Mike Dolan, Markets Editor EMEA. (Reporting by Atul Prakash; Editing by Richard Balmforth)