WASHINGTON —  Three State Department officials resigned under pressure Wednesday, less than a day after a damning report blamed management failures for a lack of security at the U.S. diplomatic mission in Benghazi, Libya, where militants killed the U.S. ambassador and three other Americans on Sept. 11.

The resignations came as lawmakers expressed anger and frustration over the findings of an independent review panel, and the State Department struggled to find a balance between protecting its diplomats while allowing them to do their jobs connecting with people in high-risk posts.

An Obama administration official said Eric Boswell, the assistant secretary of state for diplomatic security, Charlene Lamb, the deputy assistant secretary responsible for embassy security, and an unnamed official with the Bureau of Near East Affairs, had stepped down. The official spoke on condition of anonymity because he wasn’t authorized to discuss personnel matters publicly.

The department declined immediate comment on the resignation of the officials whose decisions had been criticized in the unclassified version of the Accountability Review Board’s report that was released late Tuesday.

The board’s co-chairman, retired Adm. Mike Mullen, told reporters that the board had not determined that any officials had “engaged in willful misconduct or knowingly ignored his or her responsibilities,”

But Mullen, a former Joint Chiefs of Staff chairman,  added, “We did conclude that certain State Department bureau level senior officials in critical levels of authority and responsibility in Washington demonstrated a lack of leadership and management ability appropriate for senior ranks in their responses to security concerns posed by the special mission.”

Mullen said the mission’s security fell through bureaucratic cracks caused in part because buildings were categorized as temporary. The report said that budget constraints had caused some officials to be more concerned with saving scarce money than in security.

Co-chairman Thomas Pickering, a retired ambassador, said the personnel on the ground in Benghazi had reacted to the attack with bravery and professionalism. But, he said, the security precautions were “grossly inadequate” and the contingent was overwhelmed by the heavily armed militants.

“They did the best they possibly could with what they had but what they had wasn’t enough,” Pickering said.

Pickering and Mullen spoke shortly after briefing members of Congress in private. Lawmakers from both parties emerged from the sessions with harsh words for the State Department.

“My impression is the State Department clearly failed the Boy Scout motto of be prepared,” said Sen. John Barrasso, R-Wyo.

“They failed to anticipate what was coming because of how bad the security risk already was there. ... They failed to connect the dots,” he said. “They didn’t have adequate security leading up to the attack and once the attack occurred, the security was woefully inadequate.”

Rep. Adam Schiff, a member of the House intelligence committee, said security was “plainly inadequate, intelligence collection needs to be improved, and our reliance on local militias was sorely misplaced.

“These are not mistakes we can afford to make again,” he said.

The House intelligence committee chairman, Rep. Mike Rogers, R-Mich., said the report laid bare “the massive failure of the State Department at all levels, including senior leadership, to take action to protect our government employees abroad,” and complained that no one was being held accountable.

Rogers also said he was dissatisfied with the lack of progress in finding the attackers.

Lamb, the deputy assistant secretary of state for diplomatic security who was in charge of embassy protection, testified in October before the House Oversight and Government Reform Committee and defended the security measures.

“I made the best decisions I could with the information I had,” Lamb said at the time. “We had the correct number of assets in Benghazi at the time of 9/11.”

She also told Rep. Dan Burton, R-Ind., that she rejected requests for more security in Benghazi, instead training “local Libyans and army men” to provide security, a policy in force at U.S. diplomatic facilities around the world.

Pickering and Mullen set the stage for public hearings set for Thursday on Capitol Hill., Scheduled to testify were Deputy Secretary of State William Burns, who is in charge of policy, and Deputy Secretary of State Thomas Nides, who is in charge of management.

Secretary of State Hillary Rodham Clinton was to have appeared at Thursday’s hearings, but canceled after fainting and sustaining a concussion last week while recovering from a stomach virus. Clinton is under doctors’ orders to rest.

Senate Republicans and Democrats said they hoped Clinton would testify on the Hill even though she is planning to step down from her Cabinet post.

In a letter that accompanied the transmission of the report to Capitol Hill, Clinton thanked the board for its “clear-eyed, serious look at serious systemic challenges” and said she accepted its 29 recommendations to improve security at high-threat embassies and consulates.

She said the department had begun to put in place some of the recommendations. They include increasing by several hundred the number of Marine guards stationed at diplomatic missions throughout the world; relying less on local security forces for protection at embassies, consulates and other offices; and increasing hiring and deployment of highly trained Diplomatic Security agents at at-risk posts.

Clinton agreed with the panel’s finding that Congress must fully fund the State Department’s security initiatives. The panel found that budget constraints in the past had led some management officials to emphasize savings over security, including rejecting numerous requests from the Benghazi mission and the embassy in Tripoli for enhanced protection.

House and Senate negotiators working on a defense bill agreed on Tuesday to fund 1,000 more Marines at embassy security worldwide.

The report singled out the Bureau of Diplomatic Security and the Bureau of Near East Affairs for criticism. It said there was a lack of cooperation and confusion over protection at the mission in Benghazi, a city in eastern Libya that was relatively lawless after the revolution that toppled Libyan leader Moammar Gadhafi.

But it broke little new ground about the timeline of the Benghazi attack. Killed were U.S. Ambassador Chris Stevens, information specialist Sean Smith, and former Navy SEALs Glen Doherty and Tyrone Woods — who were contractors working for the CIA. Stevens was the first U.S. ambassador killed since 1988.

The board determined that there had been no immediate, specific tactical warning of a potential attack on the 11th anniversary of Sept. 11, 2001. But the report said there had been several worrisome incidents before to the attack that should have set off warning bells.

It did confirm, though, that contrary to initial accounts, there was no protest outside the facility.

In the immediate aftermath of the attack, administration officials linked the attack to the spreading protests that had begun in Cairo earlier that day over an American-made, anti-Islamic film. Those comments came after evidence already pointed to a distinct militant attack in Benghazi.

U.N. Ambassador Susan Rice appeared on numerous TV talk shows the Sunday after the attack and used the administration talking points linking it to the film. An ensuing brouhaha in the heat of the presidential campaign eventually led her to withdraw her name from consideration to replace Clinton as secretary of state in President Barack Obama’s second term.

Sen. Jim Inhofe, R-Okla., emerging from the Senate briefing on the report, kept up the congressional criticism of Rice.

“Now we all know she had knowledge. She knew what the truth was. It was a cover-up,” he said.

While criticizing State Department management in Washington along with the local militia force and contract guards that the mission depended on for protection, the report said U.S. personnel on the ground in Benghazi “performed with courage and readiness to risk their lives to protect their colleagues in a near-impossible situation.”

It said the response by Diplomatic Security agents on the scene and CIA operatives at a nearby compound that later came under attack itself had been “timely and appropriate” and absolved the military from any blame. “There was simply not enough time for armed U.S. military assets to have made a difference,” it said.

The report also discounted speculation that officials in Washington had refused appeals for additional help after the attack had begun.

The report said the evacuation of the dead and wounded 12 hours after the initial attack was due to “exceptional U.S. government coordination and military response” that helped save the lives of two seriously wounded Americans.

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Associated Press writers Donna Cassata and Kimberly Dozier contributed to this report.