Aug 15 (Reuters) - An analyst at Fitch Ratings warned that U.S. banks, including JPMorgan Chase (JPM.N), could be downgraded if the agency further cuts its assessment of the operating environment for the industry, according to a report from CNBC on Tuesday. In June, Fitch lowered the score of the U.S. banking industry's "operating environment" to AA- from AA, citing pressure on the country's credit rating, gaps in regulatory framework and uncertainty about the future trajectory of interest rate hikes. Another one-notch downgrade, to A+ from AA-, would force Fitch to reevaluate ratings on each of the more than 70...