* Q3 net up 2.8 pct at 28.6 bln yuan vs 29.2 bln consensus
* 9-mth EBITDA margin steady at 51.3 pct vs 51.6 pct in H1
* 9-mth ARPU flat at 75 yuan/month
* Shares down 0.7 pct ahead of results; underperform in Q3 (Recasts, adds comments)
By Kirby Chien
BEIJING, Oct 20 (Reuters) - China Mobile, the world's largest mobile carrier, faces little profit growth in the coming quarters as costs to build a new 3G network weigh and increasing competition push it towards lower value subscribers.
Profits for China's top three mobile carriers have been under pressure since late last year when China Mobile and its two main rivals, China Unicom and China Telecom, embarked on a $58.5 billion plan to build new networks capable of carrying more data and multimedia content.
China Mobile reported its first year-on-year profit decline in years in the second quarter, after Beijing raised the number of mobile carriers to three from two in an industry-wide overhaul.
China Mobile is the largest by number of subscribers, with more than 500 million customers -- more than the combined populations of the United States, Germany and Britain.
It eked out a slight year-on-year profit increase in the third quarter, but analysts say its profits will remain largely flat over the next two years before it realises any benefits from more sophisticated and profitable 3G services.
The company could post 2 percent net profit growth for all 2009 and the same for the next two years due to slow take-off for its 3G system, which is based on a homegrown standard known as TD-SCDMA, said Daiwa Securities analyst Marvin Lo.
"People are still looking for profit catalysts, which are not easy to find," said Lo. "3G takeoff usually takes at least three years and may need larger handset subsidies."
China Mobile and its peers also face margin pressure as they dip deeper into China's less affluent countryside for growth due to saturation in more prosperous big cities.
The company added on average 5.68 million new users each month in January-September.
RETURN TO PROFIT GROWTH
China Mobile on Tuesday posted third quarter profits that rose 2.8 percent to 28.6 billion yuan ($4.2 billion), from 27.9 billion yuan a year ago, according to Reuters calculations from nine month figures.
The results, however, fell short of the $29.2 billion yuan forecast in a Reuters poll of six analysts.
China Telecom reported its third-quarter net profit tumbled 48 percent as users of its core fixed-line services continued to migrate to mobile services.
China Mobile's monthly average revenue per user (ARPU) -- a key measure of performance -- was steady at 75 yuan.
Its margin on earnings before interest, tax, depreciation and amortisation (EBITDA) in the first three quarters was 51.3 percent, down from 51.6 percent in the first half, but better than the second quarter.
"The EBITDA margins actually rose from the previous quarter, so that's good news. But there is still pressure on margins," said Victor Yip from UOB Kay Hian based in Hong Kong.
"We still need to see fourth-quarter numbers when all three carriers' 3G services become fully commercial."
Reflecting heightened competition in the mobile landscape, China Mobile said it will continue to increase its investments in sales channels, customer service, network optimisation and research and development to enhance its competitiveness.
The share price performance of the country's three telcoms carriers all lagged the 8.16 percent gain on Hong Kong's China Enterprises Index during the third quarter.
Only China Unicom shares ended the quarter in the positive, with a 7 percent gain -- boosted by the promise of selling Apple's iPhone -- while China Mobile fell 2.6 percent and China Telecom lost 5.2 percent. ($1=6.83 yuan) (Reporting by Kirby Chien; Graphics by Catherine Trevethan; Editing by Doug Young and Lincoln Feast)