WASHINGTON — North Korea’s reported nuclear test has again put President Bush on the defensive about Iraq: this time over accusations that the war undermined his key foreign-policy goal of denying such weapons to rogue states.

By focusing on Iraq, critics said Mr. Bush diverted America’s attention and resources from the more potent threat posed by North Korea, which announced October 9 that it had tested a weapon and may have enough plutonium for 10 bombs.

Mr. Bush “identified the right ultimate threat but he picked the wrong target,” said Graham Allison, an assistant secretary of defense in the Clinton administration who now teaches government at Harvard University in Cambridge, Mass.

At a news conference Wednesday, Mr. Bush denied that Iraq had distracted his administration. North Korea, he said, “has been trying to acquire bombs and weapons for a long period of time, long before I came into office.”

Almost immediately after September 11, 2001, Mr. Bush said stopping terrorists from acquiring nuclear materials from nations such as North Korea, Iraq and Iran would be the centerpiece of his foreign policy. “The United States of America will not permit the world’s most dangerous regimes to threaten us with the world’s most destructive weapons,” he said in his 2002 State of the Union address.

By late 2002 and early 2003, the administration’s focus had shifted exclusively to building a case for an invasion of Iraq built on the premise — later disproved — that Saddam Hussein had developed banned weapons. During that period, North Korea’s leader, Kim Jong Il, withdrew from the Nuclear Non-Proliferation Treaty, forced out U.N. weapons inspectors, turned off cameras monitoring fuel rods and produced plutonium, Mr. Allison said.

“Each of those actions should have been an alarm-bell-ringing provocation, and they just passed without hardly anything happening,” Mr. Allison said. Iraq was “exhausting all the bandwidth at the top of the U.S. government,” he said.

Even though there has been no independent confirmation of North Korea’s test, the administration been subjected to persistent questions about its ability to handle the threat, particularly given its commitment in Iraq. “The United States is quite capable of taking care of several problems simultaneously,” Secretary of State Rice said October 10 on CNN.

For now, Mr. Bush said yesterday that America will stick to its policy of trying to revive dormant, multinational negotiations known as the six-party talks. He rejected appeals from critics — including James Baker, secretary of state under Mr. Bush’s father, former President George H. W. Bush, and Rep. Curt Weldon, a Republican of Pennsylvania — to engage in bilateral dialogue with North Korea to persuade Kim’s regime to abandon its nuclear program.

“It didn’t work in the past,” Mr. Bush said, referring to direct talks between America and North Korea under the Clinton administration.

The six-party talks broke down in September 2005 after America, Russia, China, Japan, and South Korea offered a package of incentives to North Korea to abandon its nuclear program. North Korea walked out of the talks when America imposed new sanctions to punish it for counterfeiting.

America is banking on UN and bilateral sanctions to put pressure on North Korea. Japan announced yesterday that it would impose restrictions on the movement of goods and people to and from North Korea.

Arms-proliferation experts said those measures may not be sufficient to defuse two looming threats: the sale of a nuclear weapon to a terrorist or a rogue state, or a nuclear arms race in East Asia.

“I’m very concerned about an arms race,” a senior vice president for national security at the Center for American Progress in Washington, Joseph Cirincione, said.

Both South Korea and Taiwan abandoned nuclear weapons programs in the 1970s under pressure from America, he said, while Japan has 23 tons of weapons-grade plutonium and could produce a bomb within months.

None of North Korea’s neighbors said this week they were considering developing nuclear weapons. Still, Mr. Allison predicted,”within a decade, despite our best effort, you’ll see a nuclear-armed Japan and South Korea.”