WASHINGTON — President Obama is preparing to nominate Mayor Julián Castro of San Antonio as his new secretary of housing and urban development, elevating one of his party’s Hispanic rising stars as part of a cabinet shuffle that has possible implications for the 2016 presidential race, Democrats informed about the plans said on Saturday.

Mr. Castro, who has often been mentioned as a potential vice-presidential candidate for the Democrats, would take the place of Shaun Donovan, who is to become director of the Office of Management and Budget. That job is being vacated by Sylvia Mathews Burwell, whom Mr. Obama tapped to be secretary of health and human services and who seems headed to Senate confirmation.

Mr. Castro, 39, won national attention in 2012 as the keynote speaker at the Democratic National Convention, and he and his twin brother, Representative Joaquin Castro, have become popular speakers on the party’s fund-raising circuit. Mr. Obama and the Democrats have predicated their electoral hopes on appealing to the country’s growing Hispanic population as House Republicans have blocked their efforts to overhaul the immigration system.

Mr. Obama’s failure to push through immigration legislation has increased the political pressure on him and his Democratic allies from some Latino groups, which have demanded in recent weeks that the president act to reduce deportations that break up immigrant families.