By Jack Kim

SEOUL (Reuters) - Former U.S. President Bill Clinton made a surprise visit to North Korea on Tuesday to try to win the release of two jailed U.S. journalists, a move some analysts said could mark the isolated state's return to dialogue over nuclear weapons.

Clinton's trip follows months of military provocations by the impoverished North which has turned its back on negotiations with regional powers, including the United States and China, to convince it to give up ambitions to build an atomic arsenal.

North Korea's KCNA news agency said the country's chief nuclear negotiator, Kim Kye-gwan, was among those greeting Clinton -- whose administration was reported to have considered bombing the North's Yongbyon atomic plant in the early 1990s.

"As soon as he arrives, he will be entering negotiations with the North for the release of the female journalists," South Korea's Yonhap news agency quoted a source as saying.

The two U.S. journalists -- Euna Lee and Laura Ling, of U.S. media outlet Current TV co-founded by Clinton's vice president Al Gore -- were arrested on the North Korea-China border in March, accused of illegal entry and being "bent on slander".

Last month, a North Korean court sentenced them each to 12 years hard labor for what it called grave crimes.

Many analysts predicted that Pyongyang would use the journalists as leverage to drag concessions out of the U.S. administration which led pressure for U.N. sanctions on the North for its nuclear test in May.

"There is the possibility of a dramatic turnaround by North Korea that could lead to a new phase of negotiations," said Yun Duk-min of the Institute of Foreign Affairs and National Security in Seoul.

But latest trade data suggests that the North may be resorting increasingly to barter trade to make it more difficult for the international community to pressure Pyongyang through sanctions.

It is the second time a former U.S. president has headed to the communist state to try to defuse a crisis. Former president Jimmy Carter flew there in 1994 when tensions were running high, again over the North's nuclear weapons program.

"While the mission is in progress, we will have no comment," a senior U.S. official traveling with U.S. Secretary of State Hillary Clinton said. "Our interest here is the successful completion of the mission and the safe return of the journalists."

Hillary Clinton, on her way to Kenya for a trade conference, incurred the fury of Pyongyang's leaders last month by likening them to unruly children demanding attention, adding that they did not deserve it.

"SENDING THE WRONG SIGNALS"

However, one analyst said that was exactly what the former president's visit was doing -- rewarding "bad behavior".

It comes at a time of mounting speculation over succession in Asia's only communist dynasty with a number of reports suggesting that an increasingly frail-looking Kim Jong-il, 67, has settled on his third son to take over.

"It's just what they (North Korea's leaders) need," said B.R. Myers, an expert on the North's state ideology at the South's Dongseo University.

It allows the government to show to a domestic audience, facing deepening poverty, that the nuclear weapons program is making the outside world take it more seriously and the visit will be certain to be portrayed as tribute by the United States.

And it will confirm to North Korea that its bad behavior will continue to be rewarded, Myers said. "It sends all the wrong signals."

Bill Clinton, while in office, had sought to improve ties with the North, exchanging high-level envoys near the end of his term that fueled expectations that Washington and Pyongyang would end decades of hostility and normalize ties.

His Secretary of State, Madeleine Albright, visited Pyongyang in 2000 and held talks with the North's supreme leader, Kim Jong-il.

The rapid improvement in ties was short lived as George W. Bush became U.S. president and declared the North part of an "axis of evil" along with Iran and Iraq. (Additional reporting by Lucy Hornby in Beijing and Sue Pleming en route to Kenya; Editing by Nick Macfie)