* Japanese, South African candidates fall short in vote
* New contenders have a month from Monday to enter race
* Stalemate highlights rich-poor divide at IAEA
(Adds ElBaradei comment, paragraph 8, edits)
By Mark Heinrich and Sylvia Westall
VIENNA, March 27 (Reuters) - U.N. nuclear watchdog governors failed to agree on a successor to Director-General Mohamed ElBaradei on Friday after five rounds of voting, opening the field to new candidates who might bridge rich-poor divisions.
The International Atomic Energy Agency was keen to avoid a long delay installing a new chief as it confronts mounting challenges, including Iran's disputed pursuit of nuclear technology that could yield atomic bombs and a shortage of money needed to uphold its anti-proliferation mandate.
Yukiya Amano, 61, Japan's envoy to the IAEA, was the favourite but fell one vote short of the two-thirds majority required in the final vote by the IAEA's 35-nation Board of Governors against South Africa's Abdul Samad Minty, 69.
Voting was split largely along rich and poor nation lines. Industrialized states backed Amano, developing states Minty.
"The slate of candidates is considered to have been wiped clean," Ambassador Taous Feroukhi of Algeria, chairman of the Vienna-based governing board, told reporters.
New contenders -- including some Latin Americans who may be waiting in the wings -- have 28 days from Monday to throw their hats in the ring, followed by another closed-door ballot in May.
A Japanese foreign ministry official told Japanese journalists Amano would re-enter the race. Minty said he would have consultations with supporters before deciding what to do.
ElBaradei, who leaves office in November after 12 years, said he hoped for a candidate with the support of all members. "I just hope that the agency has a candidate acceptable to all...north, south, east, west because that is what is needed."
ElBaradei, who shared the Nobel peace prize with his agency in 2005, had at times tense relations with Western powers, clashing with the Bush administration over what he saw as its aggressive approach to Iran.
His critics accused him of speaking outside of his remit and being soft on countries under agency inspection -- accusations he dismissed as political attacks on the IAEA's impartiality.
"A consensus candidate (is needed), someone who doesn't mark out clear differences like this ... between the developed and developing countries. Someone for both," Feroukhi told Reuters.
The IAEA's mandate is a politically tricky balancing act -- to catch secret nuclear bomb programmes and to coordinate global cooperation in sharing nuclear energy for peaceful purposes.
Diplomats said Amano and Minty failed to convince many they could bridge disputes between industrialised member states that already have nuclear energy and developing nations pressing for a share of it despite concerns about proliferation risks.
Minty voiced bitterness at Friday's outcome. "We were hopeful that those that advocated change and a relationship with the developing world based on trust and partnership would...have implemented these noble ideals, but sadly it appears as this has only remained as good intentions," he said in a statement.
With around half-a-dozen compromise candidates waiting in the wings, Feroukhi planned consultations to see if a consensus might emerge for one candidate
Possible fresh nominees included:
* Luis Echavarri, Spanish director of the Organisation for Economic Cooperation and Development's nuclear energy agency.
* Rogelio Pfirter, Argentinean head of the Organisation for the Prohibition of Chemical Weapons in The Hague and a seasoned former nuclear treaty negotiator.
* Milenko Skoknic, Chile's ambassador to the IAEA and Feroukhi's predecessor as board chairman.
IAEA officials hope a change in U.S. foreign policy under President Barack Obama might shore up their efforts to prevent the stealthy spread of nuclear weapons technology.
Obama has signalled readiness to talk without preconditions with Iran and Syria, both subject to IAEA investigations now at an impasse, and eventually double the agency's budget. (Editing by Matthew Jones)