WASHINGTON- U.S. President Barack Obama will urge the leaders of Pakistan and Afghanistan to put aside a history of mistrust and join Washington in an alliance against Islamic extremists at a White House meeting on Wednesday, senior administration officials said.

Offering billions of dollars in U.S. military and civilian aid, Obama will warn that al Qaeda and its Taliban allies pose an existential threat and press Pakistani President Asif Ali Zardari and Afghan President Hamid Karzai to toughen their response, the officials said.

He's going to make the obvious general points that have to be said and carry such enormous weight when they are said by the president of the United States -- that these two countries have to work together for their mutual benefit, despite their history, despite the suspicions, said one official.

The White House gathering, part of Obama's new strategy for the U.S. war against al Qaeda, could produce specific agreements for cooperation on policing and border issues, the officials said.

Meetings between the three delegations begin on Wednesday morning at the State Department and continue in the afternoon with heads of government sessions at the White House. Obama will hold separate meetings with each of the leaders as well as a joint session.

Meetings continue on Thursday, with many U.S. Cabinet officials -- including interior, intelligence and agriculture -- hosting their counterparts in what one official described as an exceedingly intensive U.S. government involvement with Afghan and Pakistani leaders.

Our goal is to get the two countries to work more closely together. You can't succeed in this war given the geography unless they cooperate, the official said.

We'd like an alliance with these two countries against this kind of (extremist) threat, another official said. It's very simple ... but quite profound.

The gathering comes as the United States is pressing Zardari to deal more aggressively with the threat from the Taliban, whose movement into the Buner valley 60 miles northwest of Islamabad prompted a military offensive to eject them.

Pakistan must demonstrate its commitment to rooting out al Qaeda and the violent extremists within its borders, Richard Holbrooke, the U.S. special representative for Afghanistan and Pakistan, said on Tuesday in prepared congressional testimony.

The Taliban was driven out of Afghanistan, where it once hosted al Qaeda, by the United States and its allies after the September 11, 2001, attacks.

The group, once nurtured by Pakistan's military and intelligence services, moved into the lawless region along Pakistan's frontier and his been expanding its influence in that country as well as in Afghanistan.

NUCLEAR ARSENAL SAFE?

The United States has been pressing Pakistan to adopt a counterinsurgency approach combining both military and civilian efforts to weaken Taliban influence. That would require Pakistan to shift military focus away from its traditional enemy India.

Obama has urged the U.S. Congress to provide $1.5 billion annually for five years to help Pakistan develop roads, schools, clinics and other civilian infrastructure.

The Taliban advance toward Islamabad has alarmed U.S. officials and raised concerns about the security of Pakistan's nuclear arsenal, but Zardari said on Tuesday the atomic weapons were safe.

Zardari told CNN he would ask Obama to let Pakistan purchase pilotless U.S. drones for his military arsenal. He said he did not want Washington to use the weapons to carry out attacks on his soil and Pakistan did not need a U.S. troop presence.

U.S. forces have used drone aircraft against suspected al Qaeda leaders in Pakistan, but the attacks often kill civilians and many Pakistanis are angry the Obama administration continues to use them.

I will request the president of the United States to give it a thought that we own them (drones), then we take out our targets rather than somebody else coming and do it for us, Zardari told CNN.

U.S. officials have criticized Zardari for the weakness of his government and have met with his political opponents. But Holbrooke sent an unambiguous signal of support for the president, the widower of former Pakistani Prime Minister Benazir Bhutto who was assassinated in 2007.

We have the highest strategic interests in supporting this government, Holbrooke said in his congressional testimony. Our goal must be unambiguously to support and help stabilize a democratic Pakistan headed by its elected president, Asif Ali Zardari, he said.

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