* PM says ruling party to determine his intended departure
* Meles sees up to 2,500 foreign jihadists in Somalia
By Andrew Cawthorne
ADDIS ABABA, July 8 (Reuters) - Ethiopia's long-serving Prime Minister Meles Zenawi said on Wednesday he was looking forward to relaxing after a retirement from power that he hopes will be agreed soon with his ruling party.
"Having a long, good rest would do," the 54-year-old former rebel leader said of his plans after relinquishing the power he has held for 18 years.
In an interview with Reuters, Meles also said the arrival of jihadists from Pakistan, Afghanistan and the Gulf region had lifted the number of foreign fighters in neighbouring Somalia to anywhere between 1,000 and 2,500.
"It is a continuing influx," he said of the men coming to fight alongside Somalia's hardline insurgents.
Meles has said repeatedly he is ready to step down from the helm of sub-Saharan Africa's second most populous nation.
Most analysts believe that will be some time after an election scheduled for May 2010.
They say Meles may retain a senior post in his party or take a prominent position at an international institution given his high profile on pan-African affairs.
Declining to say when he might go, Meles did emphasise that he hoped to effect the first peaceful transition of power in Ethiopia's bloody modern history.
"It would be very important for everybody, particularly for the fledgling democratic institutions of this country."
Leaders of the ruling Ethiopian People's Revolutionary Democratic Front (EPRDF) are to meet in September in what could be a determining moment.
"The party is in the process of dialogue, and sooner or later it will make its decision, and that will be it," Meles said, adding he was unlikely to act without EPRDF blessing.
Diplomats expect the EPRDF to win the 2010 election, and for one of Meles' senior Cabinet members to take over.
"We have a large leadership pool, any one of whom could take the mantle," Meles said.
The prime minister dismissed fears of ethnic rivalry.
"That is not a prime consideration. The party has gone beyond that," said Meles, whose Tigryan community accounts for just 6 percent of the population yet dominate the country's political and military establishment.
The ethnic Amharas, who used to be Ethiopia's elite, and the country's most populous group, the Oromos, may feel it is their turn, analysts say.
Meles said he hoped a code of conduct, which the government wants to agree with the opposition, would help prevent a repeat next year of post-election violence in 2005 when 200 protesters were killed by security forces.
Media air-time and public funds for opposition parties, plus monitors from at home and abroad, should also help "level the playing-field" and ensure fair elections, said Meles.
Rights groups and opposition leaders say Meles, however, oppresses opposition, with key figures exiled or in jail.
Long anxious about the threat from Islamist militants in next-door Somalia, Meles said he did not think al Shabaab rebels would oust President Sheikh Sharif Ahmed's government even though it was close to his palace door in Mogadishu.
The presence of a 4,300-strong African Union (AU) peacekeeping force, Amisom, and the gradual building of national security forces should turn the tide, he predicted.
"There is a very serious threat to the government ... but I don't think it's about to be toppled any time soon," he said.
"I don't think al Shabaab has the capability to ride over the Amisom presence there. And together with the forces of the TFG (Transitional Federal Government), I think they will be capable of resisting the so-called final onslaught."
Meles disputed accounts from the United Nations and others of several hundred foreign fighters in Somalia.
"It's much more than that, anywhere between 1,000 and 2,500 is the estimate we have," he said.
But "it's very difficult to categorise some of these so-called foreign fighters," he said. "There are, for example, American passport holders in the Shabaab ranks, but of Somali origin. Are these foreign fighters or Somali fighters? That is a tough issue to answer. There are Canadians, and so on."
Ethiopia lost "several hundred soldiers" during its 2006-08 intervention, and has no plan to return unless there is a major threat, most notably on its border, Meles said.
The prime minister said he had conveyed that message to visiting U.S. Assistant Secretary of State for African Affairs Johnnie Carson, who was in Addis Ababa this week with a message for Ethiopia to be restrained.
"He was pushing at an open door," Meles said.
For ANALYSIS on Meles future, click on [ID:nLN889141]
For FACTBOX on Meles, click on [ID:nL855172]
For FACTBOX on possible successors, click on [ID:nL857082]
For Meles interview on G8, click on [ID:nL8703247]
For Meles interview on economy, click on [ID:nL8586492]
For Ethiopia economy FACTBOX, click on [ID:nL8442963]
(Editing by David Clarke)