Washington ? President Barack Obama’s pledge to one day rid the world of nuclear weapons runs up against global realities this week when representatives from 47 countries try to craft an agreement on keeping nuclear weapons out of terrorist hands.

Sweeping or even bold new strategies were unlikely to emerge from the two-day gathering that begins today. But Obama invited the swarm of world leaders as an important step to intensify global focus on one of the most serious nuclear proliferation threats: a world in which non-state actors — like the al-Qaida terrorist organization — obtain nuclear materials.

“The single biggest threat to U.S. security, both short-term, medium-term and long-term, would be the possibility of a terrorist organization obtaining a nuclear weapon. This is something that could change the security landscape in this country and around the world for years to come,” Obama said as he conducted a series of bilateral meetings with world leaders Sunday.

“We know that organizations like al-Qaida are in the process of trying to secure nuclear weapons or other weapons of mass destruction, and would have no compunction at using them,” Obama said.

Preventing nuclear theft

The president has set a goal of ensuring all nuclear materials worldwide are secured from theft or diversion within four years.

On the table, too, will be Iran’s perceived attempts to build a nuclear weapon in violation of the global Nuclear Nonproliferation Treaty, and North Korea’s nuclear weapons stockpile and exports of nuclear materials and technology.

“We want to get the world’s attention focused where we think it needs to be with these continuing efforts by al-Qaida and others to get just enough nuclear material to cause terrible havoc, destruction and loss of life somewhere in the world,” Secretary of State Hillary Rodham Clinton said in an interview broadcast Sunday on ABC’s “This Week.”

Clinton said the gathering would be the largest assembly of world leaders hosted by an American president since the 1945 San Francisco conference that founded the United Nations.

Obama sought to set the tone in one-on-one meetings Sunday with the leaders of India and Pakistan — antagonistic, nuclear-armed neighbors — as well as South Africa and Kazakhstan, which have given up nuclear weapons programs.

Praise for Kazakhstan

As the meetings ended, White House officials briefed reporters, paying special attention to Obama’s session with Kazakhstan President Nursultan Nazarbayev.

Michael McFaul, Obama’s senior adviser on Russia and the former Soviet Union, said the president praised Nazarbayev as “really one of the model leaders in the world. We could not have this summit without his presence.”

McFaul said Obama noted that Kazakhstan had benefited greatly on giving up its nuclear weapons when the Soviet Union collapsed in the early 1990s. That act led to “greater security and economic prosperity.” Obama said, according to McFaul, that Iran should take a lesson from Nazarbayev.

Obama also spoke about Kazakhstan’s shaky human rights record, a reminder to Nazarbayev that the United States was closely monitoring developments in that field even as it praises the country’s stand on nonproliferation.

As Obama met with South African President Jacob Zuma, Ben Rhodes, a National Security Council spokesman, said the South Africans too had set an example for their continent by giving up nuclear weapons.

Other leaders

Rhodes also announced that Obama would hold a previously unplanned sit-down with the Turkish Prime Minister Recep Tayyip Erdogan. Turkey is a key NATO ally, and relations have been difficult recently, particularly over Iran. Rhodes said there were additional “pressing issues,” including normalization of relations between Turkey and Armenia.

Obama opened Sunday’s meetings with India’s President Manmohan Singh. They covered “the range of issues,” Rhodes said, including food security, poverty reduction, the war in Afghanistan and India’s development assistance to the impoverished nation.

Israel, meanwhile, said last week that Prime Minister Benjamin Netanyahu would not attend the conference as planned. Insiders said he was worried Turkey and Egypt would use the summit to challenge him over his country’s nuclear arsenal, which the Jewish state never has acknowledged. In Netan-yahu’s absence, Israel will be represented by Deputy Prime Minister Dan Meridor.