WASHINGTON — The Clinton campaign is accusing Senator Obama of breaking a promise to Democratic voters in the first four voting states by purchasing a national television ad that will air in Florida, a state that was sanctioned by the national party.

The Obama campaign announced yesterday that it had launched a 60-second ad on CNN and MSNBC, marking the first time that either of the leading Democrats had run an ad nationwide rather than in a single state. Within hours, the Clinton campaign was crying foul, scheduling a conference call with reporters to decry the ad as a violation of the “early state pledge,” an agreement made by each candidate to avoid aggressive campaigning in the two states — Michigan and Florida — that failed to adhere to the primary calendar established by the Democratic National Committee.

“I think this calls into question whether or not Senator Obama meant the pledge when he signed it, or if losing three primaries and caucuses in a row compelled him to sacrifice a part of their integrity,” a former Iowa governor who is a top Clinton supporter, Tom Vilsack, said on the call. “That’s hardly the politics of a different kind that he’s promised.”

Mrs. Clinton’s campaign hinted that it would respond with its own ads or other campaign activity, saying it was “reviewing all options.”

But it was unclear what the impact of the dispute would be, as both campaigns have said the presidential contest is now a race for delegates, and Florida has none to offer. The Democratic National Committee stripped Florida of its delegates because it scheduled its primary for January 29, in violation of the calendar rules.

A spokesman for the Obama campaign, Bill Burton, said it had received permission from the chairwoman of the South Carolina Democratic Party to air the spot. South Carolina holds its Democratic primary on Saturday; the other three early states in the pledge — Iowa, New Hampshire, and Nevada — have already voted.