* 83 pct of Japanese companies upbeat on U.S. economic outlook
Many firms see politics as risk to growth under President Trump
* More firms cautious about China outlook than U.S outlook
* Some 40 pct face delay, problems in U.S. business plans
By Tetsushi Kajimoto
TOKYO, Sept 19 (Reuters) - A vast majority of Japanese firms are upbeat about the outlook for the U.S. economy, a Reuters poll found, a reassuring sign after some market concern earlier this year that the pace of U.S. growth could be slowing.
Most also had a generally positive outlook for China's economy even if the number of companies somewhat pessimistic about prospects was higher than for the U.S. economy.
The Reuters Corporate survey showed 64 percent of Japanese companies thought the U.S. economy would keep growing at around its current pace while another 19 percent saw it expanding further. Just 17 percent saw growth peaking out or slowing.
"Given its strong fundamentals, and just looking at economic factors, the U.S. economy should continue to expand," a manager at an electrical machinery maker wrote.
But like many other respondents, the manager also expressed concern about how well U.S. President Donald Trump's administration would handle key policy issues.
"If the U.S. government malfunctions, that will affect the economy," the manager wrote.
The survey was conducted Aug. 30-Sept. 12, during which U.S. second-quarter GDP was revised higher on robust consumer spending and strong business investment. Hurricane Harvey slammed into Texas just before the poll while Hurricane Irma hit Florida at the tail end of the survey.
Prior to the survey, economists were paring their GDP forecasts ever so slightly but better economic indicators since then have led to upward revisions.
A Reuters September poll of nearly 100 economists showed they expect the U.S. economy to expand at an annualized 2.6 percent in this quarter and 2.5 percent in the next, up from previous predictions in August of 2.5 and 2.4 percent.
In the Reuters Corporate survey, 59 percent of Japanese firms with direct or indirect dealings with U.S. businesses, said that their business plans were on track. But 33 percent said there were signs of delays or stagnation while another 8 percent said they would have to review their business plans.
Analysts said, however, that it was hard to say if the number experiencing delays or problems was particularly high, and that this could just be many companies taking a cautious tone.
The survey, conducted for Reuters by Nikkei Research, polled 548 big and mid-sized firms that reply on condition of anonymity. Around 250 companies answered the questions on the outlook for the U.S. economy while around 150 replied to questions about business plans.
On China, 51 percent expected the economy to grow at roughly its current pace and another 14 percent predicted growth would accelerate. But some 35 percent saw it peaking out or slowing.
Many respondents were worried about a potential slowdown after the Communist Party's autumn congress, at which President Xi Jinping is expected to tighten his grip on power.
"The focus is the autumn congress. China's underlying economy is performing more than expected thanks to government investment as the administration tries to sail through the congress," said a manager of another electrical machinery maker.
"The situation may change all at once after the congress, and it's fully thinkable the economy could decelerate."
China's economy expanded at a faster-than-expected 6.9 percent year-on-year in April-June , setting the country on course to comfortably meet its 2017 growth target of around 6.5 percent.
However, China's fixed-asset investment, factory output and retail sales all grew less than expected, data showed last week, reinforcing views that the world's second-largest economy is gradually beginning to lose steam in the face of rising borrowing costs.
(Reporting by Tetsushi Kajimoto; Additional reporting by Izumi Nakagawa; Editing by Malcolm Foster and Edwina Gibbs)