The Planning Commission on Tuesday postponed a public hearing to set a single-family residential zone designation for Midbury Street, an unincorporated part of Los Angeles County that the city may annex. Commissioners now will vote July 22 on the issue after residents have a chance to comment. The action is a proactive move to prepare for adding a new street. The City Council unanimously voted July 6 to apply to the Local Agency Formation Commission to annex Midbury Street, which has 42 homes and four vacant lots in an area just north of the city. The street could be added to Brea within a year, officials said.