The death of North Korea’s Kim Jong Il finds the United States with little knowledge of and virtually no leverage over what is to come in a country whose nuclear arsenal and belligerent foreign policy have long made it a leading threat to the West.

In a year in which dictators elsewhere have fallen like dominoes and the Obama administration has pressured strongmen still standing in places such as Iran and Syria, North Korea remains opaque and as unyielding as ever to outside influence.

No one is demanding that President Obama take a stand and declare that it is time for Pyongyang’s ruling elite to step down. Instead, the administration and the rest of the world appear to be in a holding pattern until further word — or action — emerges from North Korea after a mourning period that could last weeks or even months.

“It is scary how little we really know,” said one administration official who closely follows the region and who spoke on the condition of anonymity to discuss sensitive intelligence. “I don’t think you can overstate the concern.”

Officials said they were confident that Kim’s son and anointed heir, Kim Jong Eun, would take over. But they were less sure of his ability to “manage the military and elites who keep the Kim family in power,” another U.S. official said.

Some Republican presidential candidates seized on the death of Kim Jong Il to criticize the administration’s approach and to tout their own plans for dealing with North Korea, although they did not offer specifics.

Former Massachusetts governor Mitt Romney said in a statement that Kim’s death “represents an opportunity for America to work with our friends to turn North Korea off the treacherous course it is on and ensure security in the region.” He said the United States “must show leadership.”

Texas Gov. Rick Perry emphasized both the increased security threat from North Korea’s nuclear weapons and what he said was an unrivaled opportunity to “reunify the peninsula” now that Kim is gone.

With a near-total blackout of information from inside North Korea, the Obama administration was attempting to coordinate its response as closely as possible with Asian allies and partners and to calm a jittery South Korea.

Obama made a midnight call to South Korean President Lee Myung-bak on Sunday to reaffirm the U.S. commitment to stability on the Korean Peninsula “and the security of our close ally” in Seoul.

“The two leaders agreed to stay in close touch as the situation develops,” a White House statement said.

Secretary of State Hillary Rodham Clinton, Defense Secretary Leon E. Panetta and national security adviser Thomas E. Donilon each contacted their South Korean counterparts on Monday to “synchronize watches” and reaffirm U.S. support, a senior administration official said.

Clinton held an emergency meeting with Glyn Davies, the administration’s special representative for North Korea policy. Japanese Foreign Minister Koichiro Gemba, in Washington on a previously scheduled visit, also met with Clinton at the State Department.

“We are deeply concerned with the well-being of the North Korean people and our thoughts and prayers are with them during these difficult times,” Clinton said in a statement Monday night. “It is our hope that the new leadership of the DPRK will choose to guide their nation onto the path of peace by honoring North Korea’s commitments, improving relations with its neighbors, and respecting the rights of its people.”

Pentagon spokesman George Little said the U.S. military had not detected any “unusual North Korean military movements” connected to Kim’s death. He said force protection levels remain unchanged for the about 28,000 American troops based in South Korea.

Nuclear uncertainty

Administration officials who last week spoke of small steps toward a resumption of the six-party talks on nuclear disarmament said they expect all substantive contact with North Korea to be suspended during a period of mourning and internal upheaval.

No one knows how long this period will last. When Kim’s father and predecessor, Kim Il Sung, died in July 1994, three months of mourning passed before Pyongyang emerged to sign what was considered a breakthrough agreement to freeze construction of nuclear reactors in exchange for promised U.S. energy assistance.

That agreement fell apart in 2002, when North Korea startled U.S. negotiators by admitting that it had established a secret uranium-enrichment program, in violation of its commitment to forgo production of weapons-grade fuel.

Although Pyongyang conducted its first nuclear test in 2006, intelligence analysts remain uncertain about the basic features of the device. The uncertainty extends to the most fundamental aspects of the country’s nuclear program, which one North Korea expert described Monday as “a black hole.”

“I don’t think we even know whether they have a deployed capacity” of ready-to-use nuclear bombs, said Paul Stares, a northeast Asia expert with the Council on Foreign Relations. “As far as both the leadership chain of command, as well as the physical communications infrastructure, there’s next to nothing on that.”

Obtaining reliable intelligence about North Korea’s nuclear progress has been particularly difficult since 2003, when Kim Jong Il kicked U.N. nuclear inspectors out of the country. At the time, North Korea had enough plutonium, contained inside irradiated nuclear fuel rods, for five to eight nuclear bombs.

‘Our jaws just dropped’

The scale of the country’s uranium program was largely unknown until last year, when a U.S. scientist was invited to tour a sprawling facility in Yongbyon province, 60 miles north of the capital.

The scientist, Siegfried S. Hecker of Stanford University, said afterward that he had expected to find an outmoded facility filled with obsolete equipment. Instead, he found a sleek, industrial-scale uranium-enrichment plant containing more than 2,000 centrifuges. Weapons experts estimate that the factory can produce enough enriched uranium for one nuclear weapon a year.

“Our jaws just dropped,” Hecker said later in describing the visit.

After a second nuclear test, in May 2009, North Korean news reports bragged of “leaping progress” in the nation’s nuclear efforts, suggesting to many experts that a third nuclear test might be in the works.

The Obama administration had been optimistic that talks over the past six months would bring North Korea back to the six-party talks, which were suspended three years ago. Initial steps included an announcement, under discussion this week, that the United States would begin shipping food aid to North Korea and resume a program to recover the remains of U.S. soldiers from the Korean War.

Those agreements were to lay the groundwork for a meeting between North Korea and the United States in Beijing, perhaps as early as Thursday, to discuss a suspension of North Korea’s uranium-enrichment program and perhaps would have led to resumption of the broader talks, which include South Korea, China, Japan and Russia.

Now, the senior official said, “I think there’s almost no chance that North Korean officials at that level would be doing anything but going into their mourning period.”

Staff writers Craig Whitlock, Greg Miller and David Nakamura contributed to this report.