The speaker said the tape was made on July 20, two days before his sons Odai and Qusai were killed in a fierce attack on a villa belonging to a Saddam cousin in the northern city of Mosul.
The tape is the third purported Saddam recording to air in July. Two prior airings were likely to be authentic, according to U.S. intelligence officials.
The voice on the tape urged all of Saddam's former soldiers to take up arms against the Americans and not to cooperate with the Iraqi army being rebuilt by U.S. occupation forces.
"Today I speak in particular to ... your military honor and appeal to the promise you made to the nation and to the people," said the voice, which sounded like Saddam.
There was no way to immediately confirm it was the former dictator.
Saddam's fate has been uncertain since the war began on March 21. Twice information on his whereabouts was deemed solid enough that an airstrike was sent to kill him.
But since the war, U.S. intelligence analysts have become increasingly certain that he survived. Officials say they believe he remained in Iraq.
Commenting on the tape, Saad al-Bazaz editor of al-Zaman newspaper, who was once close to Saddam said to Al-Arabiya that the voice was Saddam's.
"Undoubtedly the tape carries Saddam's voice, this is no longer a controversial issue and should not be raised again," he said.
The voice purported to be Saddam's urged former soldiers not to lose faith.
"On April 11 and 12, we started to reorganize the (Baath) party and people to resist the enemy, and we were in contact with the men of the armed forces," the voice said. The Americans captured Baghdad on April 9.
"News of you, the men of the armed forces and the Republican Guard, reaches me. I am pleased when I hear that you are carrying out these honorable Jihad operations side by side with the brother Mujahedeen or when you are leading them in ... " Iraq's many cities.
Saddam credited the United States for telling the truth when U.S. assessments declared that the war was not yet over.
"Yes, this war has not ended. The will of the people, the government, the Baath Party is not broken. Now, with the war not over, the occupation will not be able to stabilize the country with its army which occupies our land. The will of the people will not be subdued by the enemy," the voice said.
His comments came as U.S. forces were attempting to form a new Iraqi army as well as a civil defense militia to work with the Americans.