WASHINGTON – The State Department on Thursday acknowledged weaknesses in security related to the deadly Sept. 11 assault on the diplomatic mission in Libya as a scathing independent report faulted management failures at the department.

Testifying at the first of two congressional hearings, Deputy Secretary of State William Burns said Secretary of State Hillary Rodham Clinton was putting in place 29 recommendations made by a special review board. She also is creating a position to focus on diplomatic security for high threat posts.

Clinton had been scheduled to testify before the committees but cancelled after fainting and sustaining a concussion last week while recovering from a stomach virus. Clinton is under doctors’ orders to rest. Lawmakers still want to hear her testimony.

The investigation’s conclusions and the political fallout from the attack in Benghazi led four State Department officials to resign on Wednesday.

“We learned some very hard and painful lessons in Benghazi,” Burns told the Senate Foreign Relations Committee. “We are already acting on them. We have to do better.”

Republicans tangled with the officials over whether warning signs of a deteriorating security situation were ignored and why the department didn’t ask Congress for money to boost security at the mission in the eastern Libyan city where U.S. Ambassador Chris Stevens and three other Americans were killed. Benghazi was relatively lawless after the revolution that toppled Libyan leader Moammar Gadhafi.

“We made the mistaken assumption that we wouldn’t become a major target,” Burns said.

Many Republicans have used the Libya attack to criticize the Obama administration and its response. Their opposition to U.N. Ambassador Susan Rice as a possible candidate to succeed Clinton, after Rice blamed the attack not on terrorism but on protests against an anti-Muslim film, led to Rice taking herself out of the running, even after Rice explained that she had relied on talking points drawn up by intelligence agencies.

Sen. Jim Inhofe, a Republican, ticked off a long list of incidents involving Westerners in the months before the raid, including attacks with rocket-propelled grenades and improvised explosive devices. Just two days before the Sept. 11 assault, Stevens had requested additional security.

Burns pointed out that report found no “specific tactical threat,” but said Inhofe was correct to identify a troubling pattern.

“We did not do a good enough job in trying to connect the dots,” Burns said.

In the first White House comment on the report, spokesman Jay Carney said what happened in Benghazi was “clearly unacceptable,” and problems need to be fixed.

The hearing provided an odd scene because the committee chairman, Sen. John Kerry, a Democrat, is a top candidate to replace Clinton as secretary in President Barack Obama’s second-term Cabinet. Kerry presided at the hearing, but asked no questions of officials who could be his future employees.

In an opening statement, Kerry said the department had “clear warning signs” of a deteriorating security situation before the attack. He also faulted Congress for failing to provide sufficient funds to protect facilities worldwide, forcing the department to scramble to cover security costs.

The department is seeking about $1.4 billion in next year’s budget for increased security; the money would come primarily from funds that haven’t been spent in Iraq.

The breakdown: $553 million for 35 additional Marine Security Guard detachments, $130 million for 155 diplomatic security personnel and $376 million for security upgrades and construction at new embassy compounds.

Since the attack, Democrats have complained that Republicans cut $300 million from the Obama administration’s budget request of $2.6 billion for diplomatic and embassy security this year.

Sen. Barbara Boxer, a Democrat, pointed out that the House balked at cutting money for U.S. military bands, which was about $388 million.

“We need to get our priorities straight around here and we can’t walk away and invite another tragedy, and as much as people like to say, ‘Well it’s not the money,’ it’s the money,” Boxer said. “You can’t protect a facility without the funding.”

Joining Burns on Capitol Hill was Deputy Secretary of State Thomas Nides, who is in charge of management.

Stevens was killed in the attack along with information specialist Sean Smith and former Navy commandos Glen Doherty and Tyrone Woods, who were contractors working for the CIA. Stevens was the first U.S. ambassador killed in the line of duty since 1979.

An unclassified version of the report by the Accountability Review Board found “systematic failures and leadership and management deficiencies at senior levels” of the State Department meant that security was “inadequate for Benghazi and grossly inadequate to deal with the attack that took place.”

The report singled out the Bureau of Diplomatic Security and the Bureau of Near East Affairs for criticism.

Obama administration officials said those who resigned were Eric Boswell, assistant secretary of state for diplomatic security; Charlene Lamb, deputy assistant secretary responsible for embassy security; and Raymond Maxwell, deputy assistant secretary of state who oversees Libya, Algeria, Tunisia and Morocco. The officials spoke on condition of anonymity because they weren’t authorized to discuss personnel matters publicly.

Some of the three may have the option of being reassigned to other duties, said the officials.

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Associated Press writer Matthew Lee contributed to this report.