* Eighth consecutive quarter of revenue falls
* Scrapping of energy subsidies hit firm
* Loss compares with small profit last year (Adds shares, detail)
MADRID, May 7 (Reuters) - Spanish builder FCC slid to a first-quarter loss of 140 million euros ($183 million) on Tuesday, hit by slumping revenues and writedowns on its renewable energy and construction units.
Revenue fell 18.5 percent to 2 billion euros, the eighth consecutive quarter of declines as Spanish public sector contracts disappeared in a deepening recession.
Around half of the company's revenues come from Spain.
Shares in the company fell 1 percent to 7.9 euros, topping the losers' board of Spanish blue chips. The stock has underperformed the European sector by 19 percent since the beginning of the year.
FCC wrote down 112 million euros in losses in its energy unit related to the scrapping of renewable energy subsidies and a new tax on power generation, and also marked down the value of its renewable energy assets.
Writedowns in its struggling Austrian construction unit Alpine also hurt results, the firm said. Alpine has suffered like other European builders from government austerity programmes in the euro zone which have put projects on hold.
Net debt at end-March grew 2.3 percent from end-December to 7.3 billion euros.
FCC is under pressure to sell around 2.2 billion euros of assets including indebted property arm Realia in order to reduce its net debt by 2.7 billion euros by 2015 in a three-year strategic plan aimed at focusing its business on infrastructure, environmental services and water management.
($1 = 0.7659 euros) (Reporting By Sonya Dowsett; Editing by Paul Day and David Cowell)