* US halved 2017-18 ITER contribution, deadlines jeopardised
* ITER chief in US for talks with Trump administration (Adds Bigot comments)
PARIS, Dec 6 (Reuters) - ITER, an international project to build a prototype nuclear fusion reactor in southern France, said it is facing delays if the Trump administration does not reconsider budget cuts.
ITER Director-General Bernard Bigot, in Washington for talks with the U.S. administration, said the U.S. contribution had been cut from a planned $105 million to $50 million this year and its 2018 contribution from a planned $120 million to $63 million.
The United States has already spent about $1 billion on the prototype reactor and was scheduled to contribute up to another $1.5 billion through 2025, when the experimental fusion reactor is scheduled to run a first operational test.
"If we do not respect deadlines (for the first operational test) in the beginning, we cannot respect them in the end," Bigot told Reuters in a telephone interview.
Bigot said that following a letter from French President Emmanuel Macron to President Donald Trump in August, Trump had asked his administration to reconsider the issue.
"We hope for a decision this weekend or this week," he said.
The seven partners in the International Thermonuclear Experimental Reactor (ITER) - Europe, United States, China, India, Japan, Russia and South Korea - launched the project 10 years ago but it has experienced years of delays and budget overruns.
It is now halfway towards the first test of its super-heated plasma by 2025 and first full-power fusion by 2035.
Earlier this year, ITER's total budget was revised upwards from 18 to 22 billion euros ($21-26 billion).
Unlike existing fission reactors, which produce energy by splitting atoms, ITER would generate power by combining atoms in a process similar to the nuclear fusion that produces the energy of the sun.
ITER says fusion will not produce nuclear waste like fission and will be much safer to operate. But the challenges of replicating the sun's fusion process on earth are enormous and critics say that it remains unclear whether the technology will work and can eventually be commercially viable.
(Reporting by Geert De Clercq. Editing by Jane Merriman)