By John Chalmers

MANILA (Reuters) - Cambodian opposition leader Sam Rainsy on Wednesday accused Prime Minister Hun Sen of using the judiciary to crush the opposition and guarantee his own victory in 2018 elections while the country goes "down the drain" amid rampant corruption.

Speaking to Reuters in Manila, where he spends some of his time since he went into his latest period of self-imposed exile, Rainsy said he still hopes to strike a political deal with his nemesis. He said he will definitely return home just before local elections in June next year.

"Hun Sen himself realizes that he is losing ground, that the popular support the opposition enjoys is growing," Rainsy said during a break from a meeting with nearly 60 key members of his Cambodia National Rescue Party (CNRP), most of whom had flown into the Philippines' capital overnight.

"So he wants to disrupt the election process by creating an atmosphere of fear and intimidation ... This is just intimidation and an attempt to frighten the whole population not to support the opposition."

Government spokesman Phay Siphan could not be reached for comment on Wednesday.

The spokesman for Hun Sen's Cambodian People's Party denied that the government or the party uses the judiciary for political ends.

"The cases against people at the CNRP are criminal wrongdoings, and they must be held responsible before the law," said Sok Eysan, adding that Rainsy should not hope for a political deal before the 2017 vote.

Rainsy, 67, has gone into exile four times, the latest coming last November when a warrant for his arrest was issued. He flew to Paris, where he has lived for considerable periods of his adult life.

He said that since then Hun Sen, who has led the country for three decades altogether, has used the judiciary to hound opposition politicians to avoid a rerun of the 2013 poll. The CNRP says it won and that the result was fixed to keep it out of power.

"The judiciary in Cambodia is just a political tool for the ruling party to ensure impunity for themselves and to crack down on the opposition," said Rainsy, wearing a garland of jasmine flowers presented to him for the party meeting.

"CULTURE OF VIOLENCE"

Rainsy's deputy, Kem Sokha, has been holed up in the CNRP's headquarters in Phnom Penh for more than a month to avoid arrest. Rainsy said that two of his party's lawmakers are behind bars while others face threats and live in danger.

Hun Sen, who is 63 and has said he will rule Cambodia into his seventies, portrays himself as the man who saved Cambodia from the terror and chaos of the Khmer Rouge years in the 1970s and the civil war that followed.

However, his authoritarian rule and widespread corruption have alienated young people who did not live through that era. Rainsy said 70 percent of the country's population are under the age of 30, and for the vast majority of them there are no jobs.

Kem Sokha told Reuters at the weekend there must be "national reconciliation" talks to end a crisis that both he and Hun Sen have warned could nudge the Southeast Asian nation from political tension into conflict.

Rainsy echoed his deputy, calling for "a culture of dialogue" to replace a "culture of violence" that he said was a legacy of the Khmer Rouge.

Nevertheless, he said he was confident that Hun Sen would allow him to return and lead the opposition party in the 2017 local communes election and general election the following year. Otherwise, the polls would not be seen by the international community as legitimate, Rainsy said.

If the opposition wins the 2018 election, Hun Sen would have no choice but to stand aside, he said.

"I think that Hun Sen is intelligent enough to understand that the world has changed, that he cannot try to cling to power forever and at any cost," Rainsy said. "All previous dictators have stepped down at one point of time."

(Reporting by John Chalmers. Editing by Bill Tarrant.)