WASHINGTON (AP) -- In a further sign of strain in U.S.-China relations, Defense Secretary William Cohen has dropped plans to visit China next month. ``It probably is not the easiest time to visit China,'' Cohen spokesman Kenneth Bacon said Tuesday, alluding to heightened tensions over alleged Chinese espionage at U.S. nuclear weapons laboratories and Chinese outrage over the mistaken American bombing May 7 of the Chinese Embassy in Belgrade. Shortly after the Chinese Embassy bombing, Beijing informed the Clinton administration that it was suspending high-level military contacts at least through May. The first casualty was a planned visit to China in mid-May by Gen. Charles Krulak, the Marine Corps commandant. Last week, China refused to allow U.S. warships entry into Hong Kong harbor. It barred a scheduled May 21 port visit by an American submarine and ship, marking the first time since World War II that the U.S. Seventh Fleet has been denied access to the former British colony. Bacon said China did not tell Cohen he was unwelcome, but the secretary decided on his own to postpone the trip. It is the second time this year Cohen has put off a trip to China. In April, he cited the urgency of the NATO air campaign over Kosovo, then in an early stage. The trip was tentatively rescheduled for June, suggesting the Clinton administration had expected the air campaign to be over by then, or nearly so. Bacon said Cohen hoped to reschedule a China trip but would be preoccupied with other matters in June. ``Right now he feels that his place is here in Washington, devoting as much time as possible to running the U.S. participation in the air campaign in Kosovo, preparing for the peacekeeping force, et cetera,'' Bacon said. Tensions with China are a factor, too. ``China, as you know, has broken off military-to-military relations temporarily with the United States, and he feels that it may be better to go later,'' Bacon said. ``He remains, of course, steadfastly committed to engagement with China as a long-term policy.'' The June trip was never officially announced, but Cohen told a congressional committee two weeks ago that he was planning to go. In his only trip to China as defense secretary, in January 1998, Cohen signed an agreement on maritime cooperation and also urged the Chinese to be more open about their military planning and strategies. -=-=- 