WASHINGTON — South Carolina Republicans pushed up their 2008 presidential primary to January 19, an earlier-than-planned date that provokes a dramatic shift in the nominating calendar and could mean the first votes are cast in December 2007.

New Hampshire is sure to follow suit to protect its first-in-the-nation primary status, and Iowa, home to the leadoff caucuses, left little doubt that it would do whatever necessary to ensure it kicks off the nominating process as it has for three decades.

“Iowa will go first, that is the bottom line,” Governor Culver, a Democrat, said yesterday in a statement, vowing to do “everything in my power.”

South Carolina’s move — and the expected aftershocks in Iowa, New Hampshire, and other early voting states — is the latest chapter in the extraordinary movement in the presidential primary calendar for Republicans and Democrats as states such as California and New York jockey for more power in choosing the party nominees.

The ever-changing contest schedule — and the earlier start to the balloting — has created an enormous level of discomfort for national parties trying to impose discipline on the states as well as presidential campaigns trying to figure out strategies when voting could begin in just four months. “Not only is this unprecedented, what’s also unprecedented is the number of journalists who could spend Thanksgiving in Iowa and Christmas in New Hampshire,” said Ken Mehlman, a former Republican National Committee chairman and President Bush’s 2004 campaign manager.

As a deterrence, both national party committees insist they will penalize states that schedule nominating contests before February 5 by withholding half of their delegates to the conventions next summer.

But that threat has largely been ignored. States assume that, as in past elections, whoever the party nominates will take over the national committees before the conventions and won’t enforce the penalty.