Vietnam informed the United Nations today that it will make every effort to stop unsanctioned departures of "boat people" and others for a "reasonable period."

The Vietnamese decision was announced by U.N. Secretary General Kurt Waldheim at the close of a two-day, 65-nation conference here to deal with the problem of the increasing hordes of refugees from Indochina.

The Vietnamese announcement was matched by a pledge from Malaysia, the country that has borne the brunt of unwanted arrivals of the boat people, that it will declare a moratorium on pushing the refugees back into the sea..tVietnamese delegate Phan Hien said the length of the "reasonable period" was not defined and that it would be "elastic" and "pragmatic."

Most of the participants expressed satisfaction and encouragement about the outcome, but U.S. officials reacted with reserve, privately expressing skepticism about Vietnamese intentions.

The Vietnamese move constituted the first public admission by the Hanoi government that it can largely control the outflow of boat people.

The U.S. view, reinforced by the distribution to American journalists here of the draft of a State Department paper based on interviews with refugees is that the Vietnamese government has indulged in a systematic campaign of forcible expulsions of ethnic Chinese and other potentially dissident groups. The paper estimated that Vietnam made $115 million in gold last year from fees charged departing "clandestine" refugees in the form of "bribes" to police officials.

Phan Hien said Vietnam immediately would start organizing centers for deparing refugees.

U.N. Refugee Commissioner Poul Hartling said his deputy, Dale De Haan, had received assurances from the Vietnamese that people who officially apply for departure "will not be harassed." Waldheim told reporters, "I don't think there is any danger in this regard."

When a reporter suggested that the moratorium violates the U.N. Charter provisions on the right ot free emigration, Waldheim answered with obvious emotion: "There is a dilemma. There is certainly a contradiction . . . but these people are drowning in th sea. We've got to do something about it."

U.S. sources said privately that the Vietnamese pledge did not impress them because the Hanoi government still can blackmail the American and other governments by resuming the refugee tide if those governments do not respect Vietnamese demands.

U.S. congressional sources close to Sen. Edward Kennedy's refugee sub-committee said the Vietnamese are kenly aware of the precedent created by the agreement between President Lyndon B. Johnson and Fidel Castro's Cuba to airlift what Castro called Cuba's "worms" to Miami.

In line with U.S. government sources said they are giving serious consideration to a Vietnamese proposal that they send American consular officials to Saigon under the umbrella of the U.N. High Commissioner for Refugees to process emigres in an orderly way.

U.S. officials admitted privately that there could come a time relatively soon when the Carter administration's policy of "keeping the heat on Vietnam," as exemplified in Vice President Walter Mondale's speech here today, could endanger efforts at normalizing relations with Hanoi.

In a tough and heavily applauded speech, Mondale stressed the analogy between this conference at Geneva and one held in 1938, across Lake Geneva at Evian, on the fate of the Jews of Germany and Austria threatened by Hitler with extermination.

He recalled that the 32 nations at the Evian conference wound up doing nothing for the Jews despite Hitler's challenge: "I can only hope that the other world, which has such deep sympathy for these criminals, will at least be generous enough to convert this sympathy into practical aid."

Mondale spoke of Vietnam's "Callous and irresponsible policies" toward the boat people. Swallowing the strongly expressed private skepticism of U.S. administration representatives here, Mondale said before the Vietnamese moratorium announcement: "There must be an immediate moratorium on the further expulsion of people from Vietnam. We must stop the drowings and establish a humane emigration program."

The vice president paid tribute to France for proposing the idea of a six-month moratorium to gain time to organize a resettlement program for the refugees.

But other American officials daid that they doubted that the U.S. Congress would ever go along with what Vietnam seems to want: a program for the United States to accept 500,000 or 600,000 more refugees.

U.S. officials said that the Vietnamese government has told U.N. refugee authorities and others that slightly less than half of the 2 million people who want to leave Vietnam have already gone, indicating that there are still a million more refugees to come.

Mondale also:

Paid tribute to the Southeast Asian "countries of first asylum," such as Malaysia, Thailand, Singapore and Hong Kong for their "compassion" in accepting so many refugees.

Announced that the Carter administration will ask Congress for $105 million for U.N. refugee programs - almost double the current U.S. effort.

Said that "highly qualified" Peace Corps volunteers would be sent to the refugee camps of Southeast Asia.

Proposed creation of an international Refugee Resettlement Fund of $200 million to help developing countries that could not otherwise afford to take in Vietnamese refugees. He said the administration would ask Congress for $20 million for the first year of the fund if other countries match the U.S. effort.

Gave details of President Carter's announcement that the U.S. 7th Fleet would help the boat people. Mondale said that Carter has ordered four more ships of the Military Sealift Command to ge dispatched to the South China Sea to transport refugees from camps to processing centers elsewhere and to help refugees at sea.

Mondale said the president had also ordered long-range naval air patrols to find and seek help for refugee boats in trouble.

American officials said that they felt the biggest concrete offer at the conference was the Philippines' pledge of an island as a reprocessing center for 50,000 refugees.

Refugee commissioner Hartling said that pledges for final resettlement of refugees had risen to 266,000 by the end of the conference.

Waldheim also announced new negotiations with Vietnam to expand an already existing agreement it has with the refugee commissioner on legally channeling refugees.

Waldheim concluded the conference with the upbeat statement that "I am confident that we have laid the foundation for the solution of one of the most tragic experience the world has known." CAPTION: Picture 1, KURT WALDHEIM . . . 'there is a delemma'; Picture 2, Vice President Mondale is welcomed by Swiss Justice Minister Kurt Furgler, left. AP