Secretary of State Alexander M. Haig Jr. today began the task of reassuring Asian allies about the emerging U.S. arms relationship with China, pledging that no weapons will be sold to Peking without full-scale consultations with allies.

In meetings with foreign ministers of key non-Communist Asian nations here for the annual meeting of the Association of Southeast Asian Nations (ASEAN), Haig portrayed the Reagan administration's decision to drop the barriers to arms for China as a limited move. Although the Asian allies were not consulted or even informed in advance of this policy shift, the secretary of state promised that "when it comes to actual arms transfers they will be consulted," according to a senior aide to Haig.

It was unclear whether Haig's arguments and efforts were effective in easing the concerns of the Asian leaders. One of them, Foreign Minister Mochtar Kusumaatmadja of Indonesia, told reporters "it kind of gave us a jolt" to learn early this week that the United States may be arming China.

The Japanese foreign minister, Sunao Sonoda, told Haig of Tokyo's approval of closer Washington-Peking ties, according to Japanese sources. But Sonoda also had some bad news for Haig, telling him in unequivocal terms that a large-scale increase in Japanese military forces being sought by the United States is impossible at this time, the sources said.

U.S. State Department and defense officials, meeting their Japanese counterparts last week in Hawaii, informally proposed increases as high as 50 percent in Japanese procurement and deployment of key weapons, according to the sources. The U.S. plan would have taken Japan's defense spending well beyond the traditional ceiling of 1 percent of that country's gross national product.

Sonoda told Japanese reporters that he counseled Haig against applying pressure for the rise in Japanese military efforts, saying: "Japanese people do not like to be pushed by others to do this or do that. What kind of roles Japan should play would be better decided by ourselves rather than outsiders."

According to Sonoda, Haig continued to urge Japan to increase its military efforts. Noting the outstanding economic growth of Japan since its defeat in World War II, Haig asked for military programs commensurate with Japan's impressive economic strength.

The meeting was Haig's first with Sonoda, a former foreign minister who was recalled to the job after the resignation of Masayoshi Ito, who had been criticized for mishandling the defense issue in the U.S.-Japan summit in Washington early last month.

Unlike some of the Southeast Asian countries, Japan is more relieved than concerned by the emerging U.S arms connection with Peking, viewing it as a sign of improvement in the recently troubled and uncertain Sino-American relations, Japanese sources said. Leaders in Tokyo reportedly feared that their own relations with China could be adversely affected by Sino-American difficulties.

The sharpest public reaction from a Southeast Asian here to the new U.S. arms sales policy came from the Indonesian foreign minister. Calling the move "a development that causes some concern," he expressed dismay that Indonesia and other members of the Association of Southeast Asian Nations (ASEAN) had not been informed beforehand.

"I would have appreciated it more if they had consulted us first," Mochtar said. He added, "I don't see how it can be helpful."

The Indonesian foreign minister said that "at this stage any supply of military equipment to China is bound to detract from the other three modernizations, which we would prefer them to concentrate on." He referred to China's policy of the "four modernizations," which calls for developing economic sectors in addition to the military.

Mochtar suggested that the policy might have an adverse effect on efforts to persuade Vietnam to reach a settlement in Cambodia, where a Hanoi-backed government is being kept in power with the support of 20,000 Vietnamese troops. Asked whether the policy could be seen as pressure on Vietnam, Mochtar said, "Hanoi may have a right to read it that way." He added that "we do not necessarily see it in that context."

ASEAN diplomats said privately that Singapore and Malaysia also were concerned by the implications of the new U.S. policy, although neither delegation would comment publicly on it.

According to U.S. officials, the policy drew no objections or serious expressions of concern in bilateral meetings today with the Japanese, Thai and Malaysian foreign ministers. One of Haig's senior ministers had "accepted and understood" the policy the way the secretary had explained it to them.

The aide said that only when the Chinese requested a particular arms sale and the United States agreed to consider it would the ASEAN countries be consulted.

"When the time comes, and it has not come, there will be consultations," the official said.

An Asian diplomat who participated in the discussions with Haig said attitudes in the region would depend in large degree on the nature of the arms being sold. "Rifles are okay, but not F15s (jet warplanes)," he said. Asian countries are counting on U.S. caution in military relations with the Chinese, the official added.

As Haig was conferring with the Southeast Asian counterparts, about 150 Filipinos, mostly students, demonstrated in front of the U.s. Embassy here to protest "U.S. imperialist domination of Third World countries."

The crowd waved banners calling for the removal of U.S. military bases in the Philippines and demanded an end to American military aid to the government of Philippine President Ferdinand Marcos.

"We call on the Filipino people to unite and dismantle the U.s.-Marcos dictatorship," said a statement issued by the group, called Youth for Nationalism and Democracy. There were no violent incidents, and the demonstrators later dispersed peacefully.