WASHINGTON — Even as the Republican presidential contenders zigzag through Iowa, New Hampshire and South Carolina, an uncertain and potentially unwieldy primary schedule in subsequent states is alarming party leaders, who fear that the voting could start earlier, last longer and complicate efforts to confront President Obama next year.

The 2012 presidential race is the first to fall under new rules from the Republican National Committee, which had intended the contests to start in February, a month later than in 2008. But at least a half dozen states are threatening to defy the rules and move up their primaries.

The result is that the first ballots are once again likely to be cast in January as Iowa, New Hampshire and South Carolina move up the dates of their contests to protect their franchises as the early voting states.

At the same time, the rush toward the front of the calendar by Florida, Michigan, Arizona, Colorado, Georgia and Missouri is accompanied by another trend: several states are pushing back their presidential primaries — or canceling them entirely — because of tight state budgets.