Greece to launch major oil quest in early July

* Greece hopes for big offshore oil, gas finds in the west

* Plans to launch exploration tender in early July

* Oil, gas blocks to be presented in July 1-2 London conference

ATHENS, June 25 (Reuters) - Greece will invite major oil companies next month to conduct offshore test drillings, the government said on Wednesday, launching the debt-laden country's most ambitious attempt so far to develop its untapped hydrocarbon potential.

Athens has made several fruitless attempts over the past decades to find big reserves of oil or natural gas. Exploration interest revived during its debt crisis, with the cash-strapped country keen to reduce its big fuel import bill.

Several blocks covering a combined area of more than 200,000 square kilometres in the Ionian Sea and south of the island of Crete are expected to go under the hammer.

Greece has been encouraged in its quest by big offshore natural gas finds in Israel and Cyprus, nearby in the Eastern (SES: E1:5KU.SI - news) Mediterranean.

The plan has been code-named "Greece MegaProject" by Petroleum Geo (Oslo: PGS.OL - news) -Services, the Oslo-based firm which completed seismic tests there earlier this year.

Energy Minister Yannis Maniatis will present the tender and PGS's geological findings at a London conference on July 1-2, the ministry said in a statement.

"(Maniatis) and officials will have private meetings with company representatives and investors to clarify special questions," the statement said.

The ministry has described PGS's findings as "encouraging", but Energean Oil & Gas, Greece's only domestic oil producer, doubts that large deposits will be found.

Greece imports almost all its oil and natural gas and spent 15.6 billion euros ($21.2 billion) to buy foreign fuel last year, about 8.6 percent of its gross domestic product.

The "MegaProject" is not Greece's only plan to find oil. Athens earlier this month granted concessions to explore and exploit possible hydrocarbon deposits in three separate on- and offshore areas to groups including Hellenic Petroleum (Athens: ELPE.AT - news) , Energean, Italy's Edison and Ireland (Other OTC: IRLD - news) 's Petroceltic .

Last month, Maniatis separately approved another request by Italian energy major Enel (Milan: ENEL.MI - news) to search for hydrocarbons in another three onshore blocs in the west.

($1 = 0.7355 Euros) (Reporting by Harry Papachristou, editing by William Hardy)