Vice President Kamala Harris’s campaign announced on Saturday that it was reserving $370 million in advertising to begin after Labor Day and run through the November election, including $200 million on digital ads.

The Harris campaign said it believed this was the largest digital ad reservation ever in American politics, reflecting the need to reach voters on their phones and other devices. Just $170 million is being reserved so far on television, as traditional television audiences continue to fragment and shrink.

“This is a modern campaign in 2024 and we’re not just stuck in the times of old, where 80 percent of the budget has to be on television,” Quentin Fulks, Ms. Harris’s principal deputy campaign manager, said in an interview.

The Harris campaign did not say how much it would spend in each state. But it said its purchases of television advertising would total twice what President Biden’s 2020 campaign spent in Pennsylvania and Wisconsin, four times what he spent in Georgia and six times what he spent in Nevada, the least populous of the battleground states.

The Harris campaign is advertising now in seven swing states — Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin — as part of a $150 million summer ad blitz. Mr. Fulks said advertising would continue in all of those states as well as nationally.

For now, Mr. Fulks said the campaign was focused on “aggressively defining” Ms. Harris in her early weeks as a presidential candidate.