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* H1 loss 1.23 bln eur versus 604 mln eur profit year ago
* Books net 962 mln euro charge against Iberdrola stake
* EBITDA rises 76 percent to 1.58 bln eur on Hochtief
MADRID, Aug 31 Spanish builder ACS wrote down part of its stake in power firm Iberdrola, pushing the group to a first-half loss as it returns to its construction roots after an ill-fated attempt to diversify and dodge the country's recession.
ACS posted a 1.23 billion euro ($1.54 billion) loss in the first-half after booking a 962 million euro impairment charge against the declining value of its stake of about 15 percent in Iberdrola, bought at the height of Spain's construction boom in a bid to diversify earnings and provide shelter from a downturn.
But as Spain suffers its second recession in a few years, with no end to a construction bust in sight, the company is relying on its recently consolidated investment in German affiliate Hochtief to boost earnings.
In the six months to June, ACS's earnings before interest, taxes, depreciation and amortisation (EBITDA) rose 76 percent to 1.58 billion euros, beating the maximum analyst forecast of 1.54 billion, thanks to the consolidation of Hochtief.
"The Iberdrola impairment doesn't make for a pretty picture at the bottom line but the market may reward the progress on the operating level," said Juan Rodriguez Rey, strategist at Banco Sabadell.
ACS is now valuing its Iberdrola stake at 3.7 euros, down from 7.1 euros previously, but still above the 3.09 euro level where the power firm was trading on Friday.
Net debt fell 13 percent to 8.58 billion euros at June 30 from a year ago, ACS said, helped by the sale of 3.7 percent of Iberdrola in April that marked a shift in the company's previous strategy of gaining more control over the utility.
ACS's shares were trading 1 percent lower at 15.48 euros at the open, compared with an 0.22 percent rise on Spain's blue chip index. ($1 = 0.8001 euros) (Reporting By Tracy Rucinski; Additional reporting by Jose Elias Rodriguez; Editing by Helen Massy-Beresford)