UPDATE 1-Greece to retender major construction projects-official

* Greece to retender major construction projects by mid '10

* New tenders necessary to avoid appeals - senior official

(Add more quotes, detail)

ATHENS, Nov 9 (Reuters) - Greece plans to re-launch tenders for two major construction projects to expand an Athens tollway and build an airport by the middle of next year, a senior infrastructure ministry official told Reuters on Monday.

Greece's new Socialist government, which swept to power after elections last month, vowed to boost transparency in tendering and awarding infrastructure projects.

The previous government had tendered new motorways worth 1.8 billion euros ($2.70 billion) in the greater Athens area and a 1-billion-euro airport in Kasteli, Crete.

But the official said new tenders were necessary to shield the projects from any appeals by local mayors and environmentalists.

"We hope we will have launched new tenders within the summer next year," the senior official who declined to be named told Reuters.

"We believe in the projects and they will be implemented but we have to clear them from a few problems, so that they are not blocked," the official added.

Funds of about 7.5 billion euros, mainly money from the European Union, are expected to pour into Greek infrastructure projects, including road concessions and airports, by 2014.

Construction accounts for 11 percent of Greece's GDP and new building projects are seen boosting Greece's ailing economy, which will fall into recession this year for the first time since 1993.

The official also said that a 477-million-euro submerged tunnel in the Northern Greek city of Thessaloniki was cancelled and the government would call for bids to pick an adviser for a new tender.

"We will go ahead with an international tender for a study, which will show us what we should do," the source said. "Facts have changed."

The Thessaloniki project was dropped as the Greek state and concessionaires went to arbitration after appeals by local residents and the country's archaeological council led to radical changes in the tunnel and increased its cost. (Reporting by Angeliki Koutantou)