TOKYO (AP) _ Vice President Dan Quayle on Friday denounced Cambodia's Khmer Rouge guerrilla group as ''mass murderers'' and said the non-communist resistance is the best hope for the war-torn country.

Quayle, attending a meeting of the International Democratic Union, made his comments at a news conference with other conservative politicians from around the world as Vietnamese forces were withdrawing from Cambodia.

The withdrawal poses the threat that the fanatical Khmer Rouge may eventually defeat the Vietnamese-backed Cambodian government forces and other resistance groups.

The vice president was asked how the United States could oppose Soviet aid to Cambodia's government when the aid was to be used to combat the communist Khmer Rouge, which was ousted from power after Vietnam's 1978 invasion.

Washington favors the non-communist resistance groups, led by Prince Norodom Sihanouk, and hopes the Cambodian people can determine their own future, Quayle said.

''We are very sensitive and very aware of the past atrocities that were committed by the Khmer Rouge,'' he said. ''The mass murderers of the Khmer Rouge should not and shall not return to power.''

The best course, he said, is to strive for democracy through the other resistance groups. ''The non-communist resistance offers the best hope for the future of Cambodia.''

The Khmer Rouge are blamed for killing hundreds of thousands of Cambodians in a radical campaign to create a pure communist society.

Quayle also said the United States hopes China will return to more moderate policies that prevailed before military force was used to crush pro-democracy demonstrations in June. Until China changes, he said, Washington will continue the sanctions imposed by President Bush, including a ban on high-level contacts and other measures.

''The ball is in China's court. ... Nothing has changed in China to change our policies that were clearly articulated by the president,'' Quayle said.

Japanese Prime Minister Toshiki Kaifu said his country will lift an advisory against traveling to Beijing but will not resume negotiations on economic aid until after Chinese authorities lift martial law in the capital. Japan is the source of about 80 percent of China's bilateral economic assistance.

In speeches earlier to the conference, Quayle and British Prime Minster Margaret Thatcher said it would be dangerous for the West to become complacent because of democratic reforms in the Soviet Union and other East bloc nations.

The International Democrat Union is a group of right-of-center political parties in 26 countries whose leaders meet every two years.

Mrs. Thatcher left for Moscow on Friday afternoon and is to hold talks with Soviet President Mikhail S. Gorbachev before returning to London.

Quayle is to travel Saturday to visit U.S. military bases in northern Japan, and next week he holds talks with Kaifu and other Japanese leaders before traveling to the Philippines and Malaysia.

Despite clashes in Manila on Friday between police and about 1,000 leftists who oppose Quayle's visit, a senior U.S. administration official said plans for the trip to the Philippines had not changed.