Greece will put two major listed companies, betting monopoly OPAP and refiner Hellenic Petroleum, up for sale by May to boost a much-delayed privatisation plan and help cut the country's debt, its chief privatisation official told Reuters.

Selling stakes in OPAP and Hellenic Petroleum , Greece's third and fourth biggest listed firms by market value, would be an important step for the indebted nation, which has repeatedly missed targets set by its EU and IMF lenders and needs investments to exit a deep recession.

In an interview with Reuters, the chief executive officer of Greece's privatisation agency, Costas Mitropoulos, said on Wednesday the tender for the sale of a 29 percent stake in OPAP, would be launched before national elections set to take place by early May, and concluded this year.

If elections go well, if there is a government and a clear direction ... then the perceived country risk for investors will fall to levels that will allow investment, Mitropoulos said. This means they will commit cash to the country.

The sale of OPAP, with a market value of 2.3 billion euros (1.92 billion pounds), was initially planned for last year but was pushed back to 2012 due to battered stock prices as the country struggled to avoid a disorderly default.

Investors are very interested in our assets, Mitropoulos said. They have some concerns over the situation in the country, its dynamics. We must show them our country's dynamics are turning from negative to positive.

Mitropoulos said the agency planned to invite investors to express their interest for a 35.5 percent stake in Hellenic Petroleum in May. The stake's current market value is about 580 million euros.

Last year, the country cashed in only 1.6 billion euros from state assets, half of which from selling new licences to OPAP. It has also invited bids for state lotteries and non-listed natural gas company DEPA.

Mitropoulos said Greece had agreed with the EU and the IMF on a revised target of about 3.0 billion euros from privatisation proceeds this year. It's a feasible target so far, he said.

Athens initially targeted privatisation proceeds of 50 billion euros by 2015 but cut the target to 19 billion euros after a very slow start on the programme.

The agency will push back the tender for Greek water firms EYDAP and EYATH from the second quarter to the second half of the year because of technical issues, Mitropoulos said.

With a huge portfolio of 70,000 real estate assets, the country is also looking for investors to develop the old Athens Hellenikon airport, Europe's biggest real estate project.

Hellenikon is attracting interest from all over the world, Mitropoulos said, adding that the project, with an estimated cost of about 5 billion euros, could boost growth by 0.3 percent annually and create between 6,000 and 9,000 jobs over its construction time.

($1 = 0.7564 euros)

(Editing by Ingrid Melander)