* Q2 adj EBITDA 5.03 bln euros vs 4.95 bln average in poll
* T-Mobile US biggest sales contributor
* German EBITDA slips on mobile slowdown, hiring costs
* Shares fall in early trading (Rewrites to include Germany, analyst comment, shares)
By Harro Ten Wolde
FRANKFURT, Aug 6 (Reuters) - Deutsche Telekom reported a slowdown in German mobile revenues during the second quarter, taking the shine off a 14-percent jump in core profit driven by its U.S. business.
Mobile service revenues were flat, compared with a 3 percent rise in the first quarter in Deutsche Telekom's home market, which is still its biggest profit engine.
Europe's largest telecoms operator by sales said its German business as a whole was also hit by higher costs for hiring new personnel for building out its network, resulting in a 1.4 percent drop in core profit to 2.22 billion euros ($2.42 billion), slightly below expectations.
Deutsche Telekom shares fell 1.7 percent in early trading on Thursday, underperforming the German blue-chip index which was down 0.2 percent.
Growth at T-Mobile US, of which Deutsche Telekom owns 65.7 percent and which is now its biggest unit by sales, countered the decline in Germany.
The U.S. company last week reported forecast-beating results and raised its forecast for new subscribers in 2015 for the second time this year.
Citi analyst Simon Weeden said that Deutsche Telekom had reported a "decent" quarter.
"With the stock having already reacted to strong results at TMUS, we expect a small negative reaction to weaker-than-expected domestic mobile service revenue," Weeden added.
Deutsche Telekom shares have risen by a third so far this year, outperforming the STOXX Europe 600 Telecommunications index, which has gained about a quarter.
Second-quarter earnings before interest, tax, depreciation and amortisation (EBITDA), excluding special items, rose to 5.03 billion euros, Deutsche Telekom said, beating the average forecast of 4.95 billion euros in a Reuters poll.
It said it still expected 2015 EBITDA, excluding special items, of around 18.3 billion euros at constant currencies and free cash flow of around 4.3 billion.
Based on the average dollar-euro exchange rate of 1.11 per euro in the first half of the year, adjusted EBITDA would be around 19.3 billion euros, Deutsche Telekom said.
($1 = 0.9168 euros)
(Editing by Georgina Prodhan and Pravin Char)