U.S. State Department officials said Wednesday that security levels at the U.S. consulate in Benghazi, Libya, were adequate for the threat level on the anniversary of the Sept. 11 attacks but that the compound was overrun by an "unprecedented attack" by dozens of heavily armed extremists.

The officials testified before an election-season congressional hearing on accusations of security failures at the consulate that led or contributed to the deaths of the U.S. ambassador to Libya and three other Americans last month. The officials said the number of U.S. and local security guards at the compound was consistent with what had been requested by the post.

"We had the correct number of assets in Benghazi at the time of 9/11," said Charlene Lamb, the deputy secretary of state for diplomatic security in charge of protecting American embassies and consulates around the world.

But White House spokesman Jay Carney told reporters Wednesday that in hindsight "there is no question that the security was not enough to prevent that tragedy from happening."

"There were four Americans killed," he said.

Lamb noted that there were five diplomatic security agents at the consulate at the time of the attack, along with additional Libyan guards and a rapid response team at a nearby annex.

Republican presidential nominee Mitt Romney has criticized the administration's early response to the attack and has made it a campaign issue, saying Monday that President Barack Obama has led a weak foreign policy in the Middle East and elsewhere.

Eric Nordstrom, the former regional security officer in Libya, said he had requested more security but that request was blocked by a department policy to "normalize operations and reduce security resources." Under questioning, though, he said he had sought mainly to prevent any reduction in staff, rather than have a big increase.

"I'm confident that the committee will conclude that Department of State, Diplomatic Security Service and Mission Libya officers conducted themselves professionally and with careful attention to managing people and budgets in a way that reflects the gravity of their task," Nordstrom said.

Security in Benghazi 'was a struggle'

Lamb rejected allegations from Republican lawmakers, supported by Lt.-Col. Andrew Wood, former head of a 16-member U.S. military team that helped protect the embassy in Tripoli, that an extension of Wood's mission could have made a difference during the attack.

"It would not have made any difference in Benghazi," Lamb said, pointing out that Wood's team was based in Tripoli and spent nearly all of its time there.

U.S. Ambassador to Libya Chris Stevens and three other Americans were killed during an attack on the attack on the consulate in Benghazi. (Ben Curtis/Associated Press)

Wood, a member of the Utah National Guard who left Libya in August, told the committee that the security in Benghazi "was a struggle and remained a struggle throughout my time there."

In testimony to the House Oversight and Government Reform Committee, he said that U.S. security was so weak that in April, only one diplomatic security agent was stationed in Benghazi.

However, Lamb and Under Secretary of State for Management Patrick Kennedy stressed that the regional security officer's requests for personnel had been met.

"The Department of State regularly assesses risk and allocation of resources for security, a process which involves the considered judgments of experienced professionals on the ground and in Washington, using the best information available," said Kennedy, a four-decade veteran of the foreign service.

"The assault that occurred on the evening of Sept. 11, however, was an unprecedented attack by dozens of heavily armed men," he said.

Republicans, Democrats spar ahead of election

The attack on the consulate and the Obama administration's evolving explanations of what happened have become a political football in the run-up to November's presidential election with Democrats saying that Republicans are trying to use a tragedy to score partisan points.

In statements immediately after the attack, neither President Barack Obama nor Secretary of State Hillary Rodham Clinton mentioned terrorism. And both gave credence to the notion that the attack was related to protests about an anti-Islam video.

"Some have sought to justify this vicious behavior as a response to inflammatory material posted on the internet," Clinton said on the night of the attack. "The United States deplores any intentional effort to denigrate the religious beliefs of others. Our commitment to religious tolerance goes back to the very beginning of our nation. But let me be clear: There is never any justification for violent acts of this kind."

The committee hearing followed assertions late Tuesday by the State Department that it never concluded that the Sept. 11 attack stemmed from protests over a privately made video that is provocative and offensive to Muslims. That had been the initial explanation offered by some in the administration, including U.S. Ambassador to the United Nations Susan Rice, before officials said it had been a planned terrorist attack.

Some Republicans have focused on the shift, suggesting that the administration was trying to cover up that it was unprepared for the 11th anniversary of the Sept. 11, 2001, terrorist attacks.

In Wednesday's hearing, Kennedy said officials, including Rice, relied on the assessments of intelligence officials in offering public explanations for the attack.