[Bolivian mayor assaulted after being kidnapped by antigovernment protesters in postelection mayhem.]

“Bolivians are upset over fraud and we will not be silent in the face of injustice,” said Diego Tamayo, 26, a university student leader who has been protesting against the government. “Never in my life have I seen a mobilization of this scale.”

It seemed uncertain that the audit would ease tensions.

Mr. Mesa has said he does not see the audit as a viable way to resolve the dispute and has urged his supporters to remain mobilized on the streets.

Mr. Arequipa, the La Paz political analyst, said that as a growing number of Bolivians have become convinced that the election was rigged, they are engaging in acts of civil disobedience not seen since an outbreak of political violence in 2003 that paved the way for Mr. Morales’s first victory.

Despite the protests, Mr. Morales retains broad popular support . Yet a letter released by members of the armed forces on Wednesday night signaled a striking level of dissent among midlevel military officers.

The letter, which is unsigned, asserts that it represents the views of 2,933 officers from the Army, Air Force and Navy. It warns that the armed forces are unwilling to crack down on anti-government demonstrations.

“The armed forces of the state will never take up arms against the people,” the officers said in the letter, which was addressed to Mr. Morales and the top leaders of the military. “Our weapons will only be raised to defend our people, our Constitution and our laws.”