Mr. Clapper’s warning, delivered in his annual worldwide threat assessment to the Senate Armed Services Committee, came a day after President Obama called the leaders of Japan and South Korea to reassure them after a satellite launch by North Korea deepened fears that the North could strike the two countries with nuclear-tipped ballistic missiles.
“Pyongyang continues to produce fissile material and develop a submarine-launched ballistic missile,” Mr. Clapper said. “It is also committed to developing a long-range nuclear-armed missile that’s capable of posing a direct threat to the United States, although the system has not been flight tested.”
In his testimony, Mr. Clapper put North Korea at the top of his list of nuclear- and proliferation-related threats. American intelligence agencies say that North Korea has expanded its uranium-enrichment facility at its main nuclear complex in Yongbyon and restarted a plutonium production reactor. North Korea “could begin to recover plutonium from the reactor’s spent fuel within a matter of weeks to months,” Mr. Clapper said.
Mr. Clapper sounded less worried about Iran, which for years topped most lists of nuclear threats. He said there was no evidence so far that Iran had breached the terms of last summer’s nuclear agreement with the West, and the deal “should serve as a tempering factor for other countries” in the Middle East, which had threatened to pursue their own nuclear-weapons programs as a deterrent to a nuclear Iran.
Still, Mr. Clapper said, “we in the intelligence community are very much in the ‘distrust, and verify’ mode.”
Iran’s leaders, he said, viewed the deal as a way to lift sanctions while preserving a nuclear capability. And Iran still has the largest inventory of ballistic missiles in the Middle East.
Nuclear proliferation was only one of a long list of threats Mr. Clapper raised, from failing states and the migration crisis to terrorist plots by the Islamic State and potential cyberattacks. “In my 50-plus years in the intelligence business,” he said, “I cannot recall a more diverse array of challenges and crises than we confront today.”
The Islamic State, in particular, has grown even more lethal, with eight branches, a skilled use of cybertools and unrivaled success in recruiting fighters. Mr. Clapper estimated that 38,200 foreigners had traveled to Syria since the start of the civil war there, including at least 6,900 from Western countries.
The director of the Defense Intelligence Agency, Lt. Gen. Vincent R. Stewart, who testified with Mr. Clapper, predicted that the Islamic State would “probably attempt to conduct additional attacks in Europe and attempt to direct attacks on the U.S. homeland in 2016.”
With North Korea testing a nuclear device and launching a satellite in quick succession, the White House has grown frustrated by its inability to curb the government in Pyongyang. Mr. Obama spoke with President Xi Jinping of China a few days before the satellite launch to urge him to use China’s influence over North Korea to prevent it.
The United States has begun negotiations with South Korea about moving equipment to place an antiballistic missile system known as the Terminal High-Altitude Area Defense System, or THAAD, on the Korean Peninsula. Installing the system has been a subject of intense debate in Seoul because it could upset an already delicate relationship with Beijing.
On Monday, the Chinese government expressed “deep concern” about the prospect of an antimissile system in the region, because the radar from such a system would penetrate its territory.
The White House has been careful not to criticize China for its failure to rein in North Korea. But Mr. Clapper emphasized that the Chinese account for 90 percent of North Korea’s trade, buying $1.2 billion worth of coal from their impoverished neighbor every year.
“To the extent that anyone has leverage over North Korea,” he said, “it’s China.”
White House officials stopped short of ranking North Korea as the world’s No. 1 proliferation threat. But with Iran in compliance with the terms of the nuclear deal, and with North Korea’s leader, Kim Jong-un, embarking on a series of provocative acts, Pyongyang has clearly supplanted Tehran as a focus for the president’s national security staff.
“Obviously, we are concerned about the risk of proliferation from North Korea,” the White House press secretary, Josh Earnest, said on Monday. “And the proliferation threat from Iran has, of course, been significantly diminished because of the international agreement to prevent them from obtaining a nuclear weapon.”
“If you were ranking them on the list and if at one point Iran were ranked above North Korea,” Mr. Earnest said, “that’s certainly no longer the case.”
In the past two years, Mr. Clapper has said that cyberattacks pose the greatest threat to the United States. In his testimony on Tuesday, he described a more subtle kind of threat, emerging from the possibility that advanced adversaries could manipulate data, everything from the guidance system for a weapon to the valves in a gas or water pipeline.
He noted that Russia was the most sophisticated cyberactor, China one of the most pervasive, and Iran and North Korea among the boldest.
For the first time Mr. Clapper also talked about how the “Internet of things” — autonomous cars, network-connected televisions and network-controlled home devices — provided “new opportunities for our intelligence collectors.”
It appeared to be a reference to the fact that the National Security Agency and domestic law enforcement agencies now have the opportunity to tap into appliances as well as phones for surveillance and, in many cases, the tracking of suspects or terrorists.