BRASILIA, Oct 27 (Reuters) - Brazil’s central bank on Wednesday raised interest rates by 150 basis points, stepping up its battle against a deteriorating inflation outlook after the government moved to loosen its constitutional spending limit. The bank’s rate-setting committee, known as Copom, decided unanimously to raise its benchmark interest rate to 7.75%. Most of the 36 economists polled by Reuters had forecast a third-straight increase of a full percentage point, but fresh fiscal concerns last week led five to expect a 125-basis-point hike and three to project an increase of 150 basis points. (Poll data reuters://realtime/verb=Open/url=cpurl%253A%252F%252Fapps.cp.%252FApps%252Fcb-polls%253FRIC%253DBRCBMP%25253DECI) Reporting by Marcela Ayres Writing by Brad Haynes Editing by Stephen Eisenhammer