BRASILIA, April 30 (Reuters) - Thousands of soccer fans could struggle to use the Internet at half of the World Cup stadiums in Brazil, a top government official said on Wednesday, underscoring the country's problems in preparing for the massive sporting event in June.

Communications Minister Paulo Bernando said that six of the 12 stadiums have not yet inked deals to install Wi-Fi networks, leaving only mobile networks available, which may not be sufficient to supply fans' demand for data capacity during games.

"Even if those stadiums sign deals now, it will be very difficult to offer good-quality service," Bernardo told reporters in Brasilia.

Preparations for the tournament, which starts on June 12, have been bogged down by a series of construction delays at stadiums and major airports, and road and transportation projects at host cities are unfinished.

Spotty cellphone coverage at key sites during the 2013 Confederation Cup, a sort of dress rehearsal for this year's World Cup, raised worries about coverage at the tournament's venues.

Wi-Fi networks at stadiums are expected to increase data capacity by as much as 50 percent.

One of the stadiums in which fans could have a hard time to upload photos or access social media is the Arena Corinthians, which will hold the World Cup's opening match, Bernardo said.

(Reporting by Alonso Soto; Editing by Prudence Crowther)