Secretary of State Cyrus Vance has appealed to Southeast Asian Nations for restraint in handling Vietnamese refugees until the world powers can devise a new plan to care for them, American officials said today.

They said Vance, who is in Japan with President Carter on his stage visit, was trying to avert more tragedies in Asian waters until a plan emerges herea at the Tokyo summit this week and at a conference of Southeast Asian nations' foreign ministers in Indonesia next week.

Yet the officials indicated today that no definite and dramatic measure has yet been devised that would satisfy the impatient demands of countries such as Malaysia and Thailand that major powers act quickly to take thousands of refugees off their hands.

They acknowledge that mere premises of eventual help probably would not deter mass evictions of refugees. In recent weeks, Thailand evicted 42,000 Cambodian refugees and Malaysia took steps to force newly arrived refugees away from its east coast.

One offical said, "If we just tell them, 'Don't push the people off,' they will be even more draconian."

The United States and Japan have agreed to make refugees a major issue at the economic summit beginning here Thursday and are hoping that European nations will show enough interest to ensure a dramatic new proposal in time for the five-nation foreign ministers' conference at Bali, Indonesia, next week.

To gain time, the sources said, Vance wrote the five foreign ministers urging restraint until a new plain is on the table.

One official paraphrased the letter as saying: "I know your situation is a crisis and we are working on the problem. Try to be cool for another week.Hang tough."

Both Thailand and Malaysia and to some extent Indonesia face internal political pressure to evict the refugees and they have recently criticized the United States and the United Nations for offering mere promises without specific action.

The United States and Japan this week have said they are considering ways to step up the permanent resettlement of refugees, increase financial contributions for their support and develop a large-scale temporary asylum someplace. They are also endeavoring to pressure Vietnam to stop the flow of boat people.

However, they declined today to say specifically what steps might be proposed at the summit and left the impression with reporters that a solution so far has not been drafted.

"We are considering an enormous number of options," said one administration oficial, emphasizing that more than 20 countries are being contacted to ensure support.

Of the seven summit nations, the United States, Canada, and France have taken large numbers of refugees, and there are reports that Britain - newly troubled by the flow of refugees into Hong Kong - is prepared to offer more assistance now. Japan has indicated it may contribute more money for resettlement but has balked at accepting any large number of refugees.

One tactic also stressed by American sources is an international effort to pressure Vietnam into cutting off the flow of refugees. They said several nations had contacted Vietnamese officials in recent weeks and said the United States has arranged "informal contacts" with the Hanoi government.

Yet one official said he believes Hanoi has made a clear decision to "clear the decks" of unwanted people, particularly of ethnic Chinese who have objected to the Communist government in the south since 1975.

He observed that nearly 60,000 reached safely by boat from Vietnam last month, compared to a monthly average of 7,500 throughout 1978.

He said the administration fears an even more dramatic exodus in coming months of Cambodian refugees fleeing into Thailand because of an impending shortage of food in wartorn Cambodia. That would probably cause Thailand - which recently expelled 42,000 Cambodians back into their country - to take drastic moves, he said.

The officials expressed little hope that a new plan negotiated with Vietnamese by the United Nations refugee officials would seriously alleviate the flow out of that country. That plan calls on Vietnam to permit an "orderly emigration" of refugees to other countries for permanent settlement.

The United States has not yet offered to accept refugees under that system. Officials explained today that the United States might accept a few through that source but does not want to give thousands of new boat people immigration slots already promised for refugees now in U.N.-sponsored camps in Thailand and Malaysia.

Carter spoke of the refugee problem today after his final bilateral meeting with Japanese Prime Minister Masayoshi Ohira.

"What we want to do," he told reporters, "is to get the entire world to participate in the acceptance of the refugees and the financing of the very expensive programs and also to get the world to induce the Vietnamese to change their policy and cut down on the large numbers who are having to leave Vietnam.

The meeting between the president and Ohira took place in a villa at Oiso, an exclusive beach resort 50 miles southeast of Tokyo.According to American officials, Carter briefed Ohira on his meeting last week in Vienna with Soviet President Leonald Brezhnev.

The two leaders also discussed the visit Carter will make later this week to South Korea, the situation in the Middle East and the refugees issue, officials said.

American officials pronounced themselves pleased with the outcome of the president's state visit to Japan. Most of the serious economic policy differences between the United States and Japan were worked out by Carter and Ohira last month in Washington, making the president's state visit the largely ceremonial occasion it was expected to be.

The only concrete result of the two days of talks announced by U.S. officials today was an agreement by the two countries to convene a meeting of nuclear safey experts to discuss existing safety programs and possible future measures.

Since the accident at the Three Mile Island nuclear power plant, Carter has stressed the importance of safety programs while in no way suggesting that the United States is ready to slow the development of atomic power.

The continued American commitment to nuclear power was reinforced today by Treasury Secretary W. Michael Blumenthal, who said he does not believe the Three Mile Island accident "will in any way significantly slow down nuclear development in the world or in the United States."

Blumenthal added that he expects the seven leaders who will meet at the economic summit to reaffirm their support for nuclear power programs.

Later today, the president paid a courtesy call on former Japanese prime minister Takeo Fukuda and attended a reception with members of the Japanese parliament.

He told the legislators his talks with Ohira were "very productive" and reaffirmed his commitment to close Japanese-American relations.

"The strength derived from friendship and close consultation permits our countries to bear the burdens of responsibility and the great and wonderful opportunities of a better life in the future," Carter said.

Tonight, the president, accompanied by his wife, Rosalynn, and daughter, Amy - both of whom appear to have recovered from a stomach virus - attended a traditional Japanese kabuki dance performance.

[On Wednesday, the president traveled to Shimoda - the fishing port where Commodore Mathew Perry landed in 1854. Carter used the occasion to hold a "town meeting," news services reported.] CAPTION: Picture 1, Vietnamese carry belongings ashore from one of the few vessels to have slipped through the naval cordon established by Malaysia to keep Indochinese refugees from its shores. In Toyko, President Carter and Premier Ohira appealed for restraint by nations facing the flood of refugees. AP; Picture 2, President Carter and Premier Ohira settle down for a second round of talks in preparation for the economic summit later this week in Tokyo. UPI