* North Korea agreed to suspend enrichment, let IAEA back
* U.N. watchdog says has no invitation from Pyongyang yet
* Unclear how much access inspectors will get (Adds quotes, detail in paragraphs 4, 11, 20)
By Fredrik Dahl
VIENNA, March 5 (Reuters) - The United Nations nuclear watchdog is preparing for a possible return to North Korea three years after its inspectors were expelled from the Asian state, but is not yet in direct contact with Pyongyang, its chief said on Monday.
Yukiya Amano, director general of the International Atomic Energy Agency (IAEA), said he needed clarification about an agreement to suspend key parts of North Korea's nuclear weapons programme that it and Washington announced last week.
"We do not have yet an invitation from North Korea," the veteran Japanese diplomat told a news conference.
"We want to know what was actually agreed between the United States and North Korea and then we have to identify the details of our possible activities in North Korea."
In last week's announcement, North Korea said it would suspend nuclear tests, long-range missile launches and enrichment of uranium at its Yongbyon nuclear facility and allow back international nuclear inspectors.
It was part of a deal with the United States that could see the eventual resumption of nuclear disarmament talks that broke down in 2008. The United States, in turn, pledged to resume food aid to the isolated and impoverished country.
It was unclear how much scope for inspections the Vienna-based U.N. agency would get. The North has limited their access during two previous periods when it allowed inspectors in.
Sceptical Western analysts have said North Korea may simply continue covert atomic activity elsewhere. Members of a U.N. expert panel said last year that North Korea most likely had several more undisclosed enrichment-related facilities.
Amano said "intensive consultations" were needed with Pyongyang and he did not rule out sending a high-level IAEA mission to the country for that purpose.
"We don't have direct contact with them but we are preparing for a possible return to Yongbyon," he said, adding that the agency's three-year absence from North Korea meant that it only had "limited" knowledge about its nuclear programme.
THIRD TIME LUCKY FOR THE IAEA?
Amano said preparatory work, including working out the details of what the inspectors would do in North Korea, could take "quite a significant amount of time."
Once this had been done, and the dispatch of inspectors was approved by the IAEA's 35-nation board of governors, they may be able to go within a few weeks, he added.
Analysts have cautioned that Pyongyang had reneged on past deals, but noted its latest move marked a sharp change in course by the North after the death in December of new leader Kim Jong-un's father, veteran strongman Kim Jong-il.
The Yongbyon complex is at the heart of North Korea's plutonium weapons programme. It includes a reprocessing plant where weapons-grade material is extracted from spent fuel rods.
In late 2010, foreign experts said North Korean officials had shown them a uranium enrichment facility at Yongbyon which potentially offered a second path to making atomic bombs.
The IAEA, whose mission is to prevent the spread of nuclear weapons in the world, is believed to have a team of inspectors who are North Korea specialists and are prepared to go to the country at short notice.
Dozens of its inspectors - who form part of a department which also has its hands full with Iran's disputed nuclear programme - have past experience of working in North Korea.
North Korea kicked out international inspectors a decade ago when a 1994 deal between Pyongyang and Washington unravelled. It expelled them again in April 2009 after rejecting the intrusive inspections provided for under a 2005 aid deal with five regional powers that allowed the U.N. watchdog to return.
"The IAEA's inspectors have remained in a state of preparedness since being asked to leave North Korea in 2009," Amano said. (Editing by Mark Heinrich)