* Brazil-born forward says wants to play for Spain
* Can't be called up until paperwork completed (Adds details, byline)
By Iain Rogers
MADRID, Oct 3 (Reuters) - Atletico Madrid's Brazil-born forward Diego Costa has expressed a desire to play for Spain but cannot be called into the squad until the necessary paperwork is completed, the nation's soccer federation (RFEF) said on Thursday.
The combative 24-year-old, who has dual Spanish and Brazilian nationality, has been on fine form this season and could bring added value to a Spain team that often plays without a traditional striker.
He tops the La Liga scoring chart with eight goals together with Barcelona's Argentina forward Lionel Messi and scored the winner in Atletico's 1-0 La Liga win at Real Madrid last weekend, their first league success against their bitter city rivals this century.
Spain coach Vicente del Bosque is due on Friday (1000 GMT) to announce his squad for the world and European champions' final two World Cup 2014 Group I qualifiers at home to Belarus on Oct. 11 and Georgia four days later.
However, Costa will have to wait to join up with the likes of Xavi, Andres Iniesta and Iker Casillas as Spain were waiting for an official document from the Brazilian soccer federation that confirmed he had never played an official match for the country of his birth.
"The Atletico Madrid player Diego Costa cannot be called up tomorrow by coach Vicente del Bosque for Spain's next matches against Belarus and Georgia as FIFA has made further demands which are in hand," the RFEF said on the national team's official website (www.sefutbol.com).
"... the player has nonetheless today made a verbal expression to the national coach of his wish to play for the Spanish national team in the future," they added.
Costa has thrived under Atletico coach Diego Simeone since the Argentine took over at the end of 2011.
He is tall and powerful in the air, has excellent touch and vision, and is always a handful for opposition defences who find it tough to cope with his physical approach that sometimes pushes the boundaries of fair play.
His first clubs in Europe were in Portugal and he moved to Atletico from Braga in 2007 before passing through Celta Vigo, Albacete, Real Valladolid and Rayo Vallecano, where he scored 10 goals in 16 La Liga appearances in 2011-12.
Last season, he was instrumental in Atletico's triumphant King's Cup campaign, scoring his eighth goal in eight appearances in the 2-1 success against Real in the final at the Bernabeu.
Spain, who will be one of the favourites at next year's finals in Brazil should they qualify as expected, lead their group on 14 points alongside France but have played one match fewer than their northern neighbours. (Editing by Justin Palmer)