Four months after North Korea defied the world by testing a nuclear device, its pledge Tuesday to close its main nuclear reactor in exchange for $400 million in aid leaves unresolved how it would abandon the rest of its nuclear facilities, weapons and atomic fuel stockpiles.

The deal, announced in a statement by the U.S. and four other nations, does not immediately require Kim Jong Il’s regime to give up any existing nuclear bombs but lays out a first deadline for key steps toward disarmament and normalized diplomatic relations.

North Korea pledged to shut down its Yongbyon nuclear reactor and permit international atomic inspectors to return to the country within 60 days. In turn, it will receive 50,000 tons of heavy fuel oil or equivalent “emergency assistance,” a down payment on a promised million tons of oil or equivalent aid when it ultimately disarms.

President Bush welcomed the nuclear deal, a rare foreign policy highlight at a time when the U.S. faces severe difficulties in Iraq and elsewhere. But administration officials also tempered expectations as some critics noted the White House previously criticized such overtures to a country the president once branded part of “the axis of evil.”

The fate of the deal may rest on whether North Korea is fundamentally prepared to renounce nuclear arms after years of delays and defiance. Pyongyang has reneged on previous agreements, and has been accused of developing its uranium-based weapons program even while freezing a plutonium-based one.

In fact, the announcement of the deal by North Korea’s official news agency said merely that the country was receiving 1 million tons of oil for a “temporary suspension” of its nuclear facilities – without mentioning the full disarmament for which the agreement calls.