* Trump administration on Friday doubled ITER 2018 budget
* US move staves off further delay to fusion project
* US has cash debt to ITER of about $120 mln for 2016-18 (Adds quotes, detail)
PARIS, March 26 (Reuters) - The United States has agreed to double its planned 2018 budget contribution to the ITER project to build a prototype nuclear fusion reactor, avoiding delays to the international project this year, its director said on Monday.
Washington cut the United States' 2017 contribution from a scheduled $105 million to $50 million and had planned to cut its 2018 contribution from a scheduled $120 million to $63 million.
But in last-minute talks about the U.S. 2018 budget last week, the U.S. Congress approved a draft Omnibus Spending Bill with a $122 million in-kind contribution for ITER, which President Donald Trump signed into law on Friday, ITER said.
"This is a very positive signal ... it will prevent ITER having to announce project delays in 2018," ITER Director-General Bernard Bigot told Reuters in a telephone interview.
He added that if the United States would make up for missing cash contributions of about $120 million for the 2016-18 period, ITER would remain on track in future years.
The International Thermonuclear Experimental Reactor (ITER) project is a cooperation between Europe, the United States, China, India, Japan, Russia and South Korea to build a prototype fusion reactor to generate electricity in a process similar to the nuclear fusion that powers the sun.
With an estimated cost of about 20 billion euros ($25 billion), the project is more than halfway towards the first test of its super-heated plasma by 2025 and first full-power fusion by 2035.
ITER member countries contributions to the project are not mainly in cash but in kind, as they finance the manufacturing of ITER components via their own national companies. These parts are then shipped to France and assembled on ITER's Cadarache, southern France site.
But there is also a cash contribution, which for the U.S. was 30-32 million euros per year in the 2016 to 2018 period, or about 100 million euros, Bigot said.
"We hope that at least maybe a small part of the U.S. 2018 contribution could be in cash so as to give a political signal to the other ITER members," said Bigot, who was appointed ITER director in 2015.
ITER's main U.S. supplier is California-based General Atomics, which is building the project's central solenoid, an 18-meter tall pillar-like magnet that will be one of the first components to be installed by 2020.
The United States has given about $1 billion to ITER so far, and had been planning to contribute an additional $500 million through 2025. ($1 = 0.8037 euros) (Reporting by Geert De Clercq Editing by Catherine Evans and Ken Ferris)