BEIJING, JULY 19 -- China, reacting to a major U.S. policy shift on Cambodia, indicated today that it will continue to support and arm the Cambodian Khmer Rouge guerrillas.

Diplomats said that Chinese officials likely were caught off guard by Secretary of State James A. Baker III's announcement Wednesday of a new U.S. policy that calls for seeking talks with Vietnam and dropping U.S. recognition of a coalition of insurgent groups that includes the Khmer Rouge.

Baker said that last year's Vietnamese troop withdrawal from Cambodia made it easier for Washington to open talks with Vietnam. But Chinese Foreign Ministry spokesman Jin Guihua said today that Vietnam had failed to withdraw all of its troops from Cambodia and must still be opposed.

"So long as Vietnam does not withdraw all its troops genuinely from Cambodia, China will continue to support the Cambodian people against the foreign invaders," Jin said at the ministry's weekly press briefing.

China is the main supporter and arms supplier of the Khmer Rouge, the strongest of three guerrilla forces fighting against the Vietnamese-installed government in Phnom Penh.

In an interview today, Cambodian Deputy Foreign Minister Sok An welcomed Baker's announcement as a "positive step that will help prevent the return of the genocidal Khmer Rouge regime to power," special correspondent Kurt Schork reported from Phnom Penh. The Foreign Ministry official indicated that he believed the U.S. initiative would force the Khmer Rouge to take the peace process more seriously.

The Khmer Rouge are regarded by many as a major obstacle to a settlement of the Cambodian conflict because of the atrocities they committed during their rule over Cambodia from 1975 to 1979. The Khmer Rouge are blamed for the deaths of up to 2 million Cambodians during that period. Vietnam invaded Cambodia in 1979 to drive the Khmer Rouge from power.

The official New China News Agency quoted resistance leaders' criticism of the U.S. decision, but the Chinese Foreign Ministry spokesman used moderate language and avoided direct criticism of the United States at today's press briefing. A Western diplomat said that it would take several days for China to provide a fuller response.

The diplomat said that it is possible that China will press for more battlefield gains in the guerrilla war against the Cambodian government. He said that the Chinese will view the U.S. policy shift as a "prize" awarded to Vietnam, which was not required to concede anything in return.

In a dispatch from Bangkok, the New China News Agency reported that the resistance forces had attacked Battambang, Cambodia's second-largest city, situated in the northwest. The agency said that the guerrilla forces held the Battambang airport for a night, but it was not possible to confirm the accuracy of the report.

Three explosions rocked Phnom Penh tonight, one near the Foreign Ministry, but police quickly cordoned of the areas, and journalists in Phnom Penh could not learn details. The blasts were followed by sporadic gunfire in the streets.

The Cambodian capital, where more than 20,000 civilians fleeing the fighting in the countryside have sought refuge in recent weeks, was under a curfew starting at 9 tonight. Battlefield gains by the resistance, which have raised the prospect that the Khmer Rouge might return to power in Phnom Penh, were a key consideration in Washington's policy about-face.

The United States has long backed the three-part coalition of the Khmer Rouge and the two non-Communist groups under Prince Norodom Sihanouk, the former Cambodian ruler, and ex-prime minister Son Sann. But under the new policy announced by Baker, the United States would withdraw its support for recognition of the coalition as the legitimate government of Cambodia that now occupies a seat at the United Nations. At the same time, the United States would continue to offer non-lethal support to the coalition and would even be prepared to increase economic support, according to Baker.

Foreign Ministry spokesman Jin said that Cambodia's U.N. seat should be retained by the coalition until a "fair, reasonable settlement" of who is to lead the Cambodian government can be reached.

Sihanouk's office in Bangkok issued a statement saying that withdrawal of the U.N. seat from the resistance coalition would send "an unprecedented wrong signal" from Washington that would not promote a settlement.

Sihanouk called the U.S. move "an act of very serious injustice" and appealed to all governments to keep Washington from trying to strip the coalition of Cambodia's U.N. seat.

Son Sann also criticized the U.S. change of policy, saying that it will have a negative effect on the peace process.