A senior Japanese diplomat has the edge over a South African rival in the contest to become the new head of the U.N. nuclear watchdog, replacing Nobel laureate Mohamed ElBaradei, diplomats say.

But Japan's Yukiya Amano cannot count on the required two-thirds majority to prevail over South Africa's Abdul Minty and succeed ElBaradei as director-general of the International Atomic Energy Agency (IAEA), the diplomats said.

Algeria, current chairman of the IAEA's Board of Governors, will start consultations shortly to gauge whether either candidate could win, diplomats said.

If not, the nomination process -- which closed on Dec. 31 -- could be reopened in the spring to attract more candidates. A new chief must be chosen at the latest by the September annual meeting of all 145 IAEA member states, who must rubber-stamp it.

ElBaradei, 66, an Egyptian who has been the head of the IAEA since 1997 and was jointly awarded the Nobel Peace Prize with the IAEA in 2005, intends to leave office after his third term expires in November.

Unresolved IAEA investigations into allegations of covert nuclear arms work in Iran and Syria during ElBaradei's tenure, and his public disputes with the United States over approach, have turned the IAEA directorship into a political hot potato.

Amano, 62, and Minty, 69, both eminent non-proliferation diplomats and negotiators who serve as their nation's ambassador to the IAEA, are lobbying hard internationally for the agency helm and claim sufficient support to win.

Amano is broadly backed by Western countries. Japan wields clout at the IAEA as the agency's second largest financier after Washington. Japan is also a leader in advancing uses of peaceful nuclear energy, the IAEA's other main brief.

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Minty, who has urged major -- mainly Western -- powers to fulfil nuclear disarmament pledges and share atomic technology for economic development, has been endorsed by the African Union and has core support in a non-aligned developing nation bloc.

"I don't see Amano getting two-thirds on the Board, at least in a first vote, but he does have more votes than Minty," said a senior NAM diplomat in Vienna, the IAEA's headquarters.

Western diplomats saw Amano as being close to two-thirds but he would need a few votes from African, Latin American or Asian board members to cross the threshold.

They are undecided and could go either way in a secret ballot, where African or other developing-nation members would not necessarily toe the line of their less than solidly united regional groupings, diplomats say.

The pivotal positions of Russia and China also were unclear.

"The balance of support seems to be with Amano but I think a third candidate is likely to emerge," a European diplomat said. In that case, diplomats say compromise entrants could include Rogelio Pfirter, head of the Organisation for the Prohibition of Chemical Weapons and a former nuclear treaty negotiator; atomic test ban treaty agency chief Tibor Toth; and Milenko Skoknic, Chile's IAEA envoy and an ex-board chairman.

The NAM diplomat said Amano and Minty both commanded distinct constituencies that could "end up blocking each other...This will not be a quick process".

ElBaradei, previously head of the IAEA's external relations office, was overwhelmingly elected director in 1997 with U.S. backing after two candidates, an Egyptian and a Swiss, fell short of a two-thirds margin in a board vote.