ISLAMABAD, Pakistan - The late U.S. envoy Richard Holbrooke's tenacity and powerful backing in Washington allowed him to weave together once-separate diplomatic efforts in Afghanistan and Pakistan. Replacing him will be difficult, international-affairs experts said Tuesday.

Holbrooke, 69, who died Monday in Washington after surgery for a tear in his aorta, had extensive experience in major posts, including Vietnam, Germany, and the former Yugoslavia.

"The office was created essentially for him and built by him to try to enable diplomatic and civilian side efforts to connect what had been two stove-piped policies under the last administration," said Daniel Markey, a South Asia expert with the Council on Foreign Relations. "Ambassador Holbrooke was playing a multilayered game. This is not an easy job."

Said Michael Corgan, a professor of international relations at Boston University: "When he spoke to the powerful in the region it was clear he had the ear of those to whom he spoke because he had the ear of the powers in Washington. There is no one on the horizon to replace him in this role."

In Afghanistan, Holbrooke was the civilian point man for the Obama administration's push to shift more responsibility to Afghan troops and the Afghan government so that U.S. troops could withdraw.

In Pakistan, Holbrooke tried to improve the U.S. image through humanitarian aid but could not fully persuade the military and government to eradicate safe havens for Taliban and al-Qaeda fighting allied troops across the border in Afghanistan.

He seemed to have reached a comfort level with Pakistan's civilian leaders, and his death could mean that the United States will have to rely more on its military-to-military contacts in the coming months to press its agenda in Islamabad, analysts said.

His efforts in Kabul faltered in part because he had a frosty relationship with President Hamid Karzai.

White House spokesman Robert Gibbs indicated Tuesday that President Obama would eventually fill Holbrooke's post as special envoy to Afghanistan and Pakistan, though he said those discussions had not begun.

Officials from Pakistan and Afghanistan issued statements of condolence Tuesday.

The praise appeared more effusive on the Pakistani side. President Asif Ali Zardari and Pakistan's ambassador to the United States, Husain Haqqani, both called him a "personal friend."

Karzai issued a brief statement calling the envoy's death "a big loss for the American people."

Holbrooke had pushed Karzai to root out the corruption that has made his government unpopular with the Afghan people and helped fuel the resurgence of the Taliban.

Holbrooke's headstrong style angered Karzai, who complained privately that the American did not understand Afghan culture.

It fell to Sen. John Kerry - and not Holbrooke - to persuade the Afghan president to agree to a runoff after the fraud-marred presidential election last year.

"I regret his death, but he had trouble here," said Farooq-e-Azam, who fought along with other U.S.-backed fighters against the Soviets. "He was not able to do well here. He could not find a language with the president."

For now, Holbrooke's death leaves Ambassador Karl Eikenberry essentially alone in conducting U.S. diplomacy with Karzai's government, and Eikenberry's relationship with Karzai is strained by his blunt assessments of the Afghan leader, revealed in leaked cables posted by WikiLeaks.