WASHINGTON—Attorney General William Barr’s review of the origins of the Russia investigation is focused in part on the U.S. intelligence assessment that found Moscow intervened in the 2016 presidential election to help then-candidate Donald Trump, according to people familiar with the matter.

Mr. Barr’s review of U.S. intelligence gathering during the probe’s early stages, announced in April, will look in particular at whether there were disagreements among the intelligence analysts who produced the findings, one of the people...