Clinton Steps Up Pressure on N. Korea : Asia: He calls sanctions ‘virtually imperative.’ Japan, S. Korea back effort against suspected nuclear program. Pyongyang insists curbs would be ‘declaration of war.’

President Clinton on Saturday stepped up efforts to increase diplomatic pressure on North Korea, calling it “virtually imperative” that the world community impose economic sanctions on Asia’s nuclear renegade.

With British Prime Minister John Major by his side during a D-day appearance in Portsmouth, England, Clinton sought to quell talk of armed conflict, saying sanctions would be “clearly . . . not an act of war and should not be seen as such.”

But North Korea’s ambassador in Beijing, Chu Chang Jun, repeated warnings Saturday that “any kind of economic sanctions” against North Korea would be regarded as “a declaration of war.”

In Washington, the United States, Japan and South Korea issued a unified call for economic sanctions after recent indications that North Korea may be concealing production of nuclear weapons.

The allies ended two days of talks Saturday, warning of “a serious situation on the North Korean peninsula,” caused by Pyongyang’s efforts to thwart inspections designed to determine how much plutonium North Korea possesses.

Assistant Secretary of State Robert L. Gallucci, flanked by a South Korean special ambassador and a senior official of the Japanese Foreign Ministry, said the three countries agreed that the U.N. Security Council must “urgently consider an appropriate response, including sanctions,” to bring North Korea to heel.

In Seoul, South Korean government officials met in an emergency session Saturday and set up a task force to assess national military readiness.

President Kim Young Sam told reporters that U.S. and South Korean forces “are keeping a round-the-clock surveillance on the North’s (military) movements,” and he added that the two allies “are fully prepared and have enough military power ready to meet any emergencies.”

The United States has about 36,000 troops and an array of sophisticated weaponry, including Patriot antimissile batteries, stationed in South Korea.

The latest swirl of rhetoric and diplomacy came two days after the director general of the International Atomic Energy Agency, Hans Blix, told members of the Security Council that North Korea had shifted spent fuel rods inside its principal nuclear reactor in ways that would obscure any efforts to divert plutonium to manufacture nuclear bombs.

The revelation deepened suspicions about North Korea’s nuclear intentions and added urgency to international efforts aimed at halting the nation’s nuclear program.

North Korea maintains that its nuclear energy facilities have not been used to make weapons.

Clinton Administration officials have said that in light of Blix’s testimony, Pyongyang should allow IAEA inspectors to take samples and measurements at the nation’s two major radioactive waste sites. That would give inspectors an alternative to analyzing spent fuel rods as a means of accounting for North Korea’s weapons-grade plutonium.

“All we want them to do is keep their word,” Clinton said Saturday. “There’s still time for North Korea to avoid sanctions actually taking effect . . . but this is in their hands.”

Washington hopes to escalate pressure gradually to persuade North Korea to let inspectors in. If Pyongyang still refuses to yield after an initial tightening of trade, the allies would press for a freeze on North Korea’s financial transactions and, finally, for a cutoff of oil and food supplies, diplomats said.

Clinton Administration officials acknowledged Saturday that negotiating a sanctions strategy that would both pinch North Korea and win the support of reluctant allies has proven a difficult and delicate task.

In an effort to win international backing for sanctions, the United States has pressed high-level contacts with Russia, as well as with China. Either country could veto any bid to impose sanctions on North Korea.

Both have been reluctant to go along with sanctions until further diplomacy has been tried. But Clinton Administration officials said they have begun to see signs of greater flexibility from both countries.

South Korea reportedly is using diplomatic channels to try to persuade China, North Korea’s last major ally, to support sanctions.

China, meanwhile, has been trying to influence North Korea to make concessions that would avoid sanctions.

On Friday, a Chinese-backed newspaper in Hong Kong said China would stop food and fuel exports to North Korea in the event of sanctions.

The Security Council may take up the sanctions matter this week.

But Russian President Boris N. Yeltsin has been pressing for a separate meeting, outside the Security Council forum, on the situation, and U.S. officials said such a huddle could “still be useful at some point.”

A senior U.S. official said Clinton and Yeltsin agreed that Secretary of State Warren Christopher and Russian Foreign Minister Andrei V. Kozyrev will get in touch to discuss “the issues involved in holding such a meeting.”