UNITED NATIONS — An upbeat State Department negotiator said yesterday that he felt a “sense of optimism” about the prospect of dismantling North Korea’s nuclear weapons program.

Assistant Secretary of State Christopher Hill, who spoke after two days of New York-style socializing and hard bargaining with Kim Jong Il’s vice foreign minister, Kim Kye Gwan, stressed that there are several differences between the Bush administration’s approach to North Korea and that of the Clinton administration.

In a briefing for reporters in New York yesterday, Mr. Hill noted that in the 1990s, America dealt with North Korea alone, while now four other powers are involved in the negotiations, including Pyongyang’s only benefactor, China. Also, tight deadlines are in place for North Korea to dismantle its weapons program in phases, he said.

Beyond the first step, in which North Korea must shut down its main plutonium production plant within 60 days in return for Western and Chinese supplies of energy resources, Mr. Hill said the object is to get the communist country to end any other nuclear designs it harbors, including undeclared uranium enrichment activities.

“We’re not in this just to shut the thing down,” he said, referring to the Yongbyon plutonium plant. “We are in this to disable it, dismantle it, grind it up, and really denuclearize the Korean peninsula.”

Under the current agreements, each phase of the denuclearization process will be monitored closely to avoid cheating, Mr. Hill said, responding to skeptics in Washington, particularly a former American ambassador to the United Nations, John Bolton.

“If there’s a problem of noncompliance, we will know it very quickly,” he said, adding that North Korea has invited the head of the International Atomic Energy Agency, Mohamed ElBaradei, for a visit next week.

The IAEA was ejected from the country last year after North Korea, whose official name is the Democratic People’s Republic of Korea, reneged on its obligations under an international treaty governing nuclear proliferation and later tested a nuclear device.

“I know there are skeptics out there. I know people have seen this issue over the years,” Mr. Hill said, adding a cautious note of his own. “The DPRK is still producing plutonium, so I think it’s a little premature to be cracking out the champagne or doing any victory laps here.”

But he said the phased approach could yield results beyond ending Mr. Kim’s declared plutoniumbased program. Despite reports last week that Washington had overstated its intelligence on the North Korean uranium enrichment program in 2002, Mr. Hill said yesterday that no final agreement would be completed without the dismantling of Pyongyang’s enrichment program.

“We cannot have a denuclearization process that leaves out HEU,” he said, using the acronym for highly enriched uranium, which can be used to make nuclear weapons.

In Washington, Deputy Secretary of State John Negroponte added that the administration has “no doubt” about the existence of a secret enrichment program, according to the Associated Press.

Under an agreement reached last month through the so-called six-party talks among North Korea, Japan, China, Russia, South Korea, and America, each of the countries was called on to complete a round of bilateral talks with Pyongyang within 30 days.

The two-day face-to-face negotiations between Messrs. Hill and Kim, which included several meals together and appearances by the North Korean diplomat at several venues around town, were the first of their kind for the Bush administration.

Relations with Japan are “very important for the DPRK’s future,” Mr. Hill said. Japan sees North Korea, which has tested missiles over Japanese territory, as a menacing neighbor.

Demilitarizing of the Korean peninsula and the rest of the region is one of the issues to be resolved. Mr. Hill said he talked at length with Mr. Kim about issues surrounding North Korea’s inclusion on the State Department’s watch list of terrorist sponsors, “including the history.”

Another thorny issue is a $20,000 account in a small, Macao-based bank, Banco Delta Asia, which reportedly belongs to Kim Jong Il, who is known in Pyongyang as the “dear leader.” Washington froze the bank’s assets after alleging that North Korea was using it to counterfeit American dollars.

“We don’t ask a lot of the world, but we do ask that you’ll not counterfeit our currency, so I don’t think there is much flexibility on that matter,” Mr. Hill said. He indicated, however, that a compromise could be reached soon.