Advertising data gathered for the New York Times by Nielsen Monitor-Plus shows that from Sept. 7 through last Thursday, Kerry had dropped seven states, including the crucial battleground of Missouri.
President George Bush and the Republican National Committee were advertising in 18 states in the same time period.
Tad Devine, a chief strategist for Kerry, said the campaign's diminished presence on television in certain states should not be seen as a sign of faltering.
"If we see an opening, we want to be able to take it," Devine said. "If the bounce continues to go down for Bush, which it will, and we come out of the debates with momentum, we'll be positioned to move."
Throughout the summer, the Bush and Kerry campaigns raised unprecedented amounts -- $242 million for Bush and $234 million for Kerry. But both candidates chose to use only $75 million of public campaign money from the close of their conventions until election day.