By Pietro Lombardi

MADRID, March 18(Reuters) - Abu Dhabi renewable energy company Masdar and Spanish power utility Endesa ELE.MC are closing in on a deal that would see Masdar pay around $200 million for a 49.9% stake in a solar portfolio controlled by Endesa, according to two sources familiar with the deal and a document seen by Reuters.

The deal for the roughly 450 megawatt portfolio builds on the existing partnership between the companies and would further expand Masdar's operations in Spain, a country it sees as key for its European growth.

"While we do not comment on market speculation, we continue to explore opportunities in the region as we expand towards our global target of 100 gigawatts by 2030," a spokesperson for state-owned Masdar said.

Endesa declined to comment.

The deal would also fit with the strategy of Italy's Enel ENEI.MI, Endesa's owner, of selling minority stakes in some projects to keep debt at bay while maintaining control of the assets.

In July last year Masdar took a minority stake in a 2-gigawatt (GW) solar portfolio controlled by Endesa.

In September it bought green energy company Saeta Yield from Canada's Brookfield BAM.TO in a $1.4 billion deal.

Masdar is controlled by UAE's power and water firm TAQA, its National oil company ADNOC and sovereign wealth fund Mubadala Investment Company.

The Masdar spokesperson referred to the previous deal with Enel, the acquisition of Saeta and that of a majority stake in Greek renewable energy company Terna as operations "further expanding our European footprint".

(Reporting by Pietro Lombardi; editing by Aislinn Laing and Susan Fenton)

((Pietro.Lombardi@thomsonreuters.com;))