Democrats will vote directly for their party's presidential primary candidates, rather than for presidential delegate slates, under a bill signed by Gov. George Deukmejian. The measure, which was backed by the State Democratic Central Committee, stipulates that the number of delegates a candidate is awarded in each of the state's 45 congressional districts will be determined by the percentage of the popular vote the candidate receives in the June 7 primary. The individual delegates will be selected at caucuses open to Democrats pledged to the various candidates. This system will replace a process used in 1984 when Democrats voted for individual delegate candidates pledged to contenders for the nomination.