The insurgent winter campaign is expected to include “attempts at high-profile attacks, attempts at targeted killings of political officials, election officials and candidates” rather than traditional battlefield engagements, the military official said.

A transparent and inclusive vote in April is viewed as central to the credibility of the Kabul government. American officials in particular had urged the Afghan government not to push the vote into summer, cautioning that any delay might make it easier for insurgents to disrupt the vote.

But the assessment shared Tuesday by the senior American officer was the first indication that the Taliban are also viewing the vote as a critical strategic point, to the degree that they would change their usual operations to focus on it.

At the same time, relations between the Afghan government and the United States are at a particularly delicate stage. A grand council, or loya jirga, of Afghan elders and powerful officials is expected to meet in coming weeks to recommend whether to accept a bilateral security agreement with the United States. If the agreement is then approved by Parliament, it will allow thousands of troops to remain after the NATO combat mission officially ends in December 2014.

There are around 50,000 American troops in Afghanistan, but that level will drop to 34,000 by February under orders from President Obama. As part of a commitment to helping the Afghans secure the elections, the number of American troops would then hold steady at the 34,000 level and not drop further until next July, according to the senior official.