On the eve of a major nuclear security summit in Washington, in which nearly 50 leaders from around the world are participating, a leading American newspaper has brought into sharp focus the operation of a new Pakistani nuclear reactor. "Three months ago, American intelligence officials examining satellite photographs of Pakistani nuclear facilities saw the first wisps of steam from the cooling towers of a new nuclear reactor," The New York Times said in a lead story on Monday. "It was one of three plants being constructed to make fuel for a second generation of nuclear arms". The newspaper did not give the location of the plant, nor quoted any official source for the story, but said "The message of those photos was clear: While Pakistan struggles to make sure its weapons and nuclear labs are not vulnerable to attack by Al Qaeda, the country is getting ready to greatly expand its production of weapons-grade fuel. The Pakistanis insist that they have no choice, according to the dispatch. A nuclear deal that India signed with the United States during the Bush administration ended a long moratorium on providing India with the fuel and technology for desperately needed nuclear power plants. Now, as critics of the arrangement point out, the agreement frees up older facilities that India can devote to making its own new generation of weapons, escalating one arms race even as President Barrack Obama and President Dmitri A. Medvedev of Russia sign accords to shrink arsenals built during the cold war. Obama met with the leaders of India and Pakistan on Sunday, a day ahead of a two-day Washington gathering devoted to the question of how to keep nuclear materials out of the hands of terrorists. In remarks to reporters about the summit meeting, Obama called the possibility of a terrorist organization obtaining a nuclear weapon represented the single biggest threat to U.S. security, both short-term, medium-term and long-term. President Obama is focusing high-level attention on the threat that already exists out there, and thats tremendously important, Sam Nunn, the former Democratic senator, was quoted as saying. But the fact is that new production adds greatly to the problem. Nowhere is that truer than Pakistan, where two Taliban insurgencies and al-Qaeda coexist with the worlds fastest-growing nuclear arsenal, The Times said. Citing a senior American official, the newspaper said Obama used his private meeting Sunday afternoon with Yousaf Raza Gilani, Pakistans newly empowered prime minister, to express disappointment that Pakistan is blocking the opening of negotiations on a treaty that would halt production of new nuclear material around the world. Citing unnamed experts, it said accelerated production in Pakistan translates into much increased risk. The challenges are getting greater the increasing extremism, the increasing instability, the increasing material, said Rolf Mowatt-Larssen of the Kennedy School of Government at Harvard, who as a C.I.A. officer and then head of the Energy Departments intelligence unit ran much of the effort to understand Al Qaedas nuclear ambitions. Thats going to complicate efforts to make sure nothing leaks, he was quoted as saying. The trends mean the Pakistani authorities have a greater challenge. In an interview with the New York Times last Monday, Obama avoided a question about his progress in building on a five-year, $100 million Bush administration programme to safeguard Pakistans arms and materials. I feel confident that Pakistan has secured its nuclear weapons, Obama said. I am concerned about nuclear security all around the world, not just in Pakistan but everywhere. He added, One of my biggest concerns has to do with the loose nuclear materials that are still floating out there. Taking up the Pakistan-India arms race at the summit meeting, according to administration officials, would be too politically divisive. Were focusing on protecting existing nuclear material, because we think thats what everyone can agree on, one senior administration official was quoted as saying. To press countries to cut off production of new weapons-grade material, he said, would take us into questions of proliferation, nuclear-free zones and nuclear disarmament on which there is no agreement. Obama plans to open the summit meeting with a discussion of the scope of the terrorist threat. The big challenge, Mowatt-Larssen said, is to get world leaders to understand that its a low-probability, but not a no-probability, event that requires urgent action. The next phase in Obamas arms-control plan is to get countries to agree to a treaty that would end the production of new bomb fuel, The Times said. Pakistan has led the opposition, and it is building two new reactors for making weapons-grade plutonium, and one plant for salvaging plutonium from old reactor fuel, it said. Last month, the Institute for Science and International Security, a private group in Washington, reported that the first reactor was emitting steam. That suggests, said Paul Brannan, a senior institute analyst, that the reactor is at least at some state of initial operation. Asked about the production, Pakistans ambassador to the United States, Husain Haqqani, said, Pakistan looks forward to working with the international community to find the balance between our national security and our contributions to international nonproliferation efforts. In private, it said, Pakistani officials insist that the new plants are needed because India has the power to mount a lightning invasion with conventional forces. India, too, is making new weapons-grade plutonium, in plants exempted under the agreement with the Bush administration from inspection by the International Atomic Energy Agency, the dispatch noted. (Neither Pakistan nor India has signed the Nuclear Nonproliferation Treaty.) The Obama administration has endorsed the Bush-era agreement. Last month, the White House took the next step, approving an accord that allows India to build two new reprocessing plants. While that fuel is for civilian use, critics say it frees older plants to make weapons fuel. The Indian relationship is a very important one, said Nunn, who influenced Mr. Obamas decision to endorse a goal of ridding the world of nuclear weapons. But he said that during the Bush years, I would have insisted that we negotiate to stop their production of weapons fuel. Sometimes in Washington, we have a hard time distinguishing between the important and the vital.