The United States is heading into a major international conference on Indochinese refugees today with new ideas for expanded rescue operations at sea and for a special air or sea lift from Asian camps to American shores.

The U.S. plans, which have been recommended to President Carter, are expected to be discussed by Vice President Mondale in the 60-nation meeting on Indochina refugees being convened today in Geneva by United Nations Secretary General Kurt Waldheim.

If approved, the new plans would supplement the major U.S. initiative last month in doubling, to 14,000, the monthly quota of Indochinese refugees accepted here. The current initiatives, like those announced previously, are intended to encourage other nations to do more in dealing with a still-growing diplomatic and humanitarian problem.

The proposals now under consideration, according to informed sources, include:

New instructions to American warships and other vessels to encourage the rescue of more "boat people" on the high seas. A proposal to assign major units of the Seventh Fleet to rescue duty has been rejected, officials said. Butliberalized rules to replace a guideline of "neither seeking nor forsaking refugees" should increase the number of U.S. military sea rescues, which added fewer that 1,200 people in the past 18 months.

The use of naval spotter planes to look for "boat people" on the high seas.

A one-time program to bring in quickly a group of 20,000 to 40,000 Indochinese through special aircraft flights or sealifts as a dramatic indication of U.S. humanitarian efforts and to relieve mounting pressure on overcrowded Asian camps. Most of those people would come to the United States anyway, a few at a time, under existing procedures.

U.S. contributions to a large new "holding camp" for Indochines refugees in Indonesia, the Phillippines or possibly China. The big Chinese island of Hainan near the Vietnamese cost is one of the areas under discussion.

As the U.S. delegation headed by Mondale departed for Geneva, a spokesman there for the U.N. high commissioner for refugees announced that various Western nations have promised to provide homes for some 250,000 Indochinese, double the number planned for resettlement at the beginning of June.

Doubling of this number is among the stated objectives of the Geneva meeting, which is designed to prove to worried Southest Asian nations that the rest of world is willing to assist in dealing with the human flood still coming out of Vietnam.

Unless the Southeast Asian nations can be convinced that held is on the way, they are likely to shut their doors and guard their waters against the tide of escaping Vietnamese, which is running well over 10,000 a week.

The United States is seeking to concentrate at Geneva on the humanitarian aspects of caring for the refugees, and leave condemnation of Vietnam and discussion of the source of the problem to a later session of the U.N. Security Council.

Vietnam's senior delegate to the Geneva meeting, Deputy Foreign Minister Phan Hien, warned at a news conference there against turning the meeting into a political forum, saying Vietnam "is not about to let itself be put before a political tribunal."

Hien said Hanoi is ready to discuss "orderly, safe and legal departure" of refugees and indicated that Vietnam may allow special transit camps on its territory. Such camps might relieve the outflow of refugees, most of whom are ethnic Chinese, but could involve troublesome international precedents regarding a nation's treatment of long-time residents.

Vietnam's great power ally, the Soviet Union, is taking part for the first time in Geneva in a conference on the Indochina refugee issue. The Russians have publicly backed the stands of the Vietnamese, but hav also indicated privately growing sensitivity about Southeast Asian nations, which are blaming of their troubles on Moscow.

China, which waged a mini-war against Vietnam early this year, made clear that it considers political questions fair game for discussion at Geneva. Han Nianlong, a senior Chinese official, charged this week that "the creation and export of millions of refugees by the Vietnamese authorities have become an international tragedy which attracts world attention."