BEIJING (AP) _ Premier Li Peng said Saturday that China will sign the nuclear non- proliferation treaty, becoming the last major nuclear power to do so and marking a significant step toward world arms-control cooperation.

The surprise announcement was made to Japanese Prime Minister Toshiki Kaifu, the first leader of a top industrialized power to visit China since it crushed a democracy movement two years ago.

Kaifu - whose nation last week marked the 46th anniversary of the two U.S. atomic bomb attacks - has been expected to press Beijing to join an international campaign to curb arms sales during the four-day visit.

Li made the announcement to Kaifu in part because Japan is the only nation to suffer a nuclear attack, Chinese Foreign Ministry spokesman Wu Jianmin told a news conference.

''China has not posed any conditions for its accession to the treaty,'' Wu said. He added that a signing date would be announced ''in due course.''

The pact limits transfer of nuclear materials and mandates inspections of nuclear facilities. China became the lone holdout among the five major nuclear powers after France agreed to the treaty's terms in June.

The United States and other nations have demanded China cooperate with international weapons-control efforts.

Wu refused to give details on why China reversed its opposition to the 23- year-old treaty, signed by 140 nations. China had previously said it did not need to sign the treaty because it already opposed proliferation of nuclear arms.

The state-run Xinhua News Agency quoted Li saying China decided to sign the treaty to promote ''comprehensive prohibition and thorough destruction of nuclear weapons.''

Beside France's support of the treaty, another factor for the switch may have been Japan's decision to link aid funds to support of global disarmament efforts.

''We are indeed very happy that the Chinese saw fit to come to this decision,'' Kaifu's spokesman, Sadaaki Numata, told a separate news conference.

''It was very important. Our people have actually experienced what it is like having nuclear weapons dropped on us,'' he said. An estimated 210,000 people died in the U.S. atomic bomb attacks on Hiroshima and Nagasaki.

The White House welcomed China's decision.

''This is something that we have been seeking for a long time,'' press secretary Marlin Fitzwater said in a statement from Kennebunkport, Maine, where President Bush is vacationing.

The West has become increasingly critical of Chinese missile sales and nuclear cooperation with developing nations. China has denied giving Algeria, Pakistan, Iraq and other Third World countries the technology or materials to build nuclear weapons. Chinese officials also contend the United States and Soviet Union sell more missiles abroad.

China's nuclear arsenal is far smaller than those of the United States, Soviet Union, Britain or France. It has about 60 single-warhead, medium-range missiles and eight single-warhead strategic missiles, according to the London- based Institute of Strategic Studies.

Kaifu met with Li in the Great Hall of the People shortly after arriving in Beijing.

The visit is a major step in China's efforts to recover from the international isolation and condemnation that followed its June 1989 crackdown that killed hundreds, and perhaps thousands, of pro-democracy demonstrators.

In addition to arms control, Kaifu is expected to press Beijing on human rights issues, trade, economic development, efforts to reduce tensions on the divided Korean peninsula and progress on Cambodian peace talks. China supports guerrillas who have waged a 12-year war against Cambodia's Vietnam-backed government.

Kaifu offered $1.5 million for the victims of floods and storms that have killed at least 2,000 people this summer. Japan already had pledged $600,000 in flood relief.

While the two leaders were meeting, China's state-run television broadcast an old black-and-white movie of Chinese guerrillas fighting Japan's invading army during World War II.

The Chinese government in the past has played upon Japan's guilt over the invasion in pressing for aid and investment, and the broadcast may have been intended to do so again.