By Marc Jones LONDON, Sept 1 (Reuters) - Credit rating agency Moody's raised its 2023 U.S. economic growth forecast on Friday but cut its estimate next year for China, saying that while the risk of a recession had fallen in the United States, China's challenges were mounting. "We have raised our growth forecast for the United States' economy to 1.9% in 2023 from 1.1% in our May outlook, acknowledging the strong underlying economic momentum," Moody's said in a report. The firm, now the only big three agency to have a top notch triple A rating for the U.S. following Fitch's downgrade last month, kept its 2024 growth forecast at 1%, saying that high interest rates would act as a brake on the economy. "We believe that it will be difficult for the Fed to achieve a sustained fall in inflation to its 2.0% target if current economic conditions persist," Moody's said. "A few quarters of below-trend growth is required, in our view, to prevent overheating."