WASHINGTON (AP) _ Secretary of State Warren Christopher expressed concern Thursday about the attempted infiltration by North Korean agents into South Korea and urged both Seoul and Pyongyang to exercise restraint.

``We wish that all parties would avoid taking any further provocative actions of the kind reflected apparently in this step,'' Christopher told a news conference.

Appearing with Christopher was Japanese Foreign Minister Yukihiko Ikeda, who said he shares Christopher's views.

``We very much hope that this incident won't develop into something that will have negative effects on the environment,'' Ikeda said.

He said it was important that nothing disrupt the agreement under which Japan, South Korea and other nations are helping North Korea abandon its plutonium-producing nuclear reactors and shift to safer models.

Ikeda said the process has become an important source for dialogue with the North Koreans.

Later, Christopher's spokesman, Nicholas Burns, issued a clarification in which he took a tougher line against North Korea than Christopher.

Burns urged North Korea ``not to engage in any provocative acts,'' adding that Christopher did not intend to direct his admonition against South Korea.

``It's very bizarre incident,'' Burns said. ``The fact that the submarine was where it was is provocative.''

Five months have passed since the United States and South Korea proposed a direct North-South dialogue with American and Chinese officials serving as mediators. North Korea has yet to give a definitive response to the proposal.

The attempted infiltration appears to be the most serious incident between the two Koreas in some time. Christopher's remarks suggested concern that South Korea might retaliate, further escalating tensions on the peninsula.

The news conference followed several hours of discussions among Christopher, Ikeda, Defense Secretary William Perry and the director general of Japan's Defense Agency, Hideo Usui.

Christopher said U.S. officials had been in touch with South Korean officials about the incident, which involved an abortive North Korean attempt to infiltrate agents via a submarine, which was found stranded off South Korea's east coast.

Christopher was cautious in his comments, noting that South Korea is still investigating the incident.

The meeting of the four cabinet level officials was the second of its kind and covered a variety of issues, including U.S. attempts to make the American military presence on Okinawa less intrusive.

Perry and Usui disclosed the possibility of creating a floating off-shore facility where the United States would be able to transfer some assets located on Okinawa. The pressure for a reduced U.S. presence there has been strong, reflected in the outcome of a recent referendum among Okinawans on the issue.

``The vision in me hopes that this floating off-shore facility will be the solution,'' Perry said. He added that as an engineer, he is aware that difficult technical problems must be overcome.

The facility is one of three options being considered as part of the effort to revamp the American presence on Okinawa, Perry and Usui said. The others involve establishing heliports at local bases.

Perry flatly denied reports that the United States is considering a reduced manpower presence on Okinawa.