Experts say 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 Department’s intelligence unit ran much of the effort to understand Al Qaeda’s nuclear ambitions.

Image President Obama met with President Hu Jintao of China during the international nuclear summit in Washington on Monday. Credit... Doug Mills/The New York Times

“That’s going to complicate efforts to make sure nothing leaks,” he said. “The trends mean the Pakistani authorities have a greater challenge.”

Few subjects are more delicate in Washington. In an interview last Monday, Mr. Obama avoided a question about his progress in building on a five-year, $100 million Bush administration program to safeguard Pakistan’s arms and materials.

“I feel confident that Pakistan has secured its nuclear weapons,” Mr. 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, administration officials say, would be “too politically divisive.”

“We’re focusing on protecting existing nuclear material, because we think that’s what everyone can agree on,” one senior administration official said in an interview on Friday. 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.”

Mr. Obama said he expected “some very specific commitments” from world leaders.

“Our expectation is not that there’s just some vague, gauzy statement about us not wanting to see loose nuclear materials,” he said. “We anticipate a communiqué that spells out very clearly, here’s how we’re going to achieve locking down all the nuclear materials over the next four years, with very specific steps in order to assure that.”