UPDATE 3-UAE's du eyes $680 mln network boost in 2010

* CEO hopeful broadband, triple-play to cover nation in 2010

* Potential infrastructure sharing deal with Etisalat in H1

* Net profit after royalty 78.55 mln dirhams, up 150 pct

* Active mobile subscribers stand at 3.139 million

* Shares close 4.9 pct down

(Adds closing share price in penultimate paragraph)

By John Irish

DUBAI, Nov 1 (Reuters) - United Arab Emirates telecoms firm du DU.DU, which posted a record quarterly profit on Sunday, plans to invest as much as 2.5 billion dirhams ($680.8 million) in 2010 as it looks to boost its services nationwide.

The operator, which broke Emirates Telecommunications Corp's (ETEL.AD) monopoly in 2007, more than doubled profit in the third quarter, driven by a 51-percent rise in active subscribers in the world's third-largest oil exporter.

"Those are very good number if we consider the seasonality of the third quarter which is summer, Ramadan and usually a slower time in the activity in the country," Chief Executive Osman Sultan said in a post-earnings conference call.

Thousands of expatriates have lost their jobs in the Gulf trade and tourism hub of Dubai since the global financial crisis took hold, hitting earnings across sectors.

Still, quarter-to-quarter net profit rose 36 percent as the operator gained 233,200 mobile telephone customers in the period. It now has 3.139 million active subscribers.

Du shares fell almost 5 percent in Dubai in line with a broad retreat across the Middle East as negative sentiment spreads over the state of the global economy.

Telecom analyst Sleiman Aboulhosn at Abu Dhabi-based Prime Emirates said du's quarterly profit was ahead of his estimates as subscriber numbers exceeded expectations.

"We saw stronger subscriber numbers and saw that with Etisalat too ... it's quite impressive," he said. Etisalat posted a 5 percent rise in third-quarter net profit in October. [ID:nLI604356]

The results were in line with analysts polled in a Reuters survey in October which forecast an average 177.4 percent rise in the quarter. [ID:nL4449450]