UPDATE 1-Spain's ACS H1 net falls 12 pct, beats forecasts

(Adds detail, background, share price)

MADRID, July 30 (Reuters) - Spain's ACS (ACS.MC: Quote, Profile, Research) posted an 11.7 percent drop in first-half net profit on Wednesday, beating forecasts, and the builder confirmed it had agreed to sell its stake in power firm Union Fenosa to Gas Natural.

ACS said Gas Natural (GAS.MC: Quote, Profile, Research) would pay it 18.33 euros per share for the 45 percent holding in Fenosa, which would net it some 7.59 billion euros and help it trim debt and fund the possible acquisition of more shares in Fenosa (UNF.MC: Quote, Profile, Research) rival Iberdrola (IBE.MC: Quote, Profile, Research).

ACS said earlier that its net profit for the first six months of the year fell to 893 million euros ($1.39 billion) from 1.01 billion a year ago, beating the average forecast from a Reuters poll of five analysts of 839 million.

The fall in H1 profit was due to tougher comparatives, as last year's figure included the proceeds from disposals, as well as costs related to investments in other companies, chiefly the raising of its stake in Germany's Hochtief (HOTG.DE: Quote, Profile, Research) to 25.1 percent.

Financing costs cut the contribution from its stakes in Abertis (ABE.MC: Quote, Profile, Research), Iberdrola (IBE.MC: Quote, Profile, Research) and Hochtief to 19 million euros from 32 million a year earlier.

Earnings before interest, tax, depreciation and amortisation (EBITDA) rose 11.7 percent to 1.91 billion euros in the first half, compared to a forecast of 1.88 billion.

ACS' value has fallen by a quarter since the start of the year, against the backdrop of a rapid slowdown in Spain's once-booming property sector.

Trading in ACS shares was suspended before Wednesday's open following press reports of a deal on Fenosa.