According to [1] San Francisco has the most police per 100,000 residents in California amongst cities with populations 100,000 or more. According to [2] this is still less than the number of police per 100,000 people in London. Given the prevalence of guns, lack of social safety net in the U.S., and overall higher rate of murders I would have thought American cities had more police than British cities. Note that police forces have gotten smaller in the UK over the last several years and they consider themselves under staffed.
[1] https://www.sfchronicle.com/crime/article/Is-the-San-Francis...
[2] https://www.finder.com/uk/police-statistics