UPDATE 2-Mobistar Q3 earnings fall short of expectations

* Q3 core profit 142.4 mln euros, vs expected 146 mln euro

* Q3 revenues 361.5 mln euros, vs expected 392 mln euros

* Keeps 2009 outlook

* Shares down 4.4 percent

(Adds detail, background)

BRUSSELS, Oct 23 (Reuters) - Mobistar (MSTAR.BR), Belgium's second biggest mobile phone operator, reported a 5.3 percent drop in third-quarter core profit, slightly worse than analysts had forecast, to end a two-month share rally.

The stock had gained some 20 percent between mid-August and mid-October, but dropped 4.4 percent to 46.7 after the results. It was the weakest in the DJ Stoxx European telecoms index .SXKP, which gained 0.9 percent.

"Mobistar has performed very well over the last months both in absolute terms and compared to the sector. They were at 42 euros (mid August) so these results are likely to put some pressure on the stock," KBC analyst Nico Melsens said.

Regulatory measures, such as lower roaming rates that came into force on July 1, pressured revenues, Mobistar said on Friday. Average third-quarter revenue per user per month fell 4.5 percent to 31.31 euros ($46.88).

July-September earnings before interest, tax, depreciation and amortisation (EBITDA) came in at 142.4 million euros, just below the 146 million forecast in a Reuters poll.

Handset sales were boosted by the new iPhone 3G (AAPL.O), for which Mobistar has exclusive rights to market in Belgium.

Mobistar, majority-owned by France Telecom (FTE.PA), repeeated its 2009 targets of stable turnover, a telephone EBITDA margin close to 40 percent, and a net profit of 240-260 million euros, implying a fall of about 10 percent from 2008.

Regulatory measures would reduce 2009 revenue by some 35 million euros, it said. ($1=0.6679 euros) (Reporting by Antonia van de Velde; Editing by Dan Lalor and Mike Nesbit)