A majority of U.N. members today adopted a declaration setting out a broad strategy to end the fighting in Cambodia and to ensure the holding of U.N.-supervised elections free from coercion by armed Cambodian factions.

The five-day U.N. General Assembly conference on Cambodia ended when 83 nations agreed to endorse a weakened version of a draft proposal put forward by the five-member Association of Southeast Asian Nations (ASEAN) and supported by the United States calling for a "comprehensive political settlement" to the conflict in the war-torn nation.

ASEAN diplomats' efforts to produce a "clear resolution" on the situation in Cambodia were blunted when China's objections forced them to abandon two key elements in their draft document. The provisions called for the need to disarm all conflicting Cambodian factions and to set up an interim government in advance of elections.

Despite the tactical concessions, the backers of the U.N. declaration said it sets the groundwork for future efforts toward a negotiated settlement. Vietnam, which forcibly installed the current Cambodian government of Heng Samrin with a 200,000-man occupation army, refused to attend the conference. The Soviet Union, which has been financially, underwriting Vietnam's war efforts, also did not come.

While there is no political solution in sight, ASEAN did open new avenues for bringing Vietnam to the negotiating table at a future date. The ASEAN-backed declaration sets out the possibility of international economic aid for Hanoi once it withdraws its troops from Cambodia and elections are held. The United States, which resists economic aid to Hanoi, will continue to mount a campaign to squeeze economically hard-pressed Vietnam even further to force it into concessions, Western diplomatic sources said.

ASEAN diplomats suggested that the respective maneuvers being mounted by the United States and ASEAN, who cooperated closely on conference preparations, could develop into a two-pronged approach to persuade Hanoi that its best long-term interests lie in ending its occupation of Cambodia. These diplomats hope that their more conciliatory posture, a departure from previous policies, will help pave the way for increasing "informal" contacts with Hanoi. The hard-line U.S. stance, meanwhile, is intended to exert the maximum political and economic pressure on Vietman.

The ASEAN nations -- Singapore, Malaysia, Thailand, Indonesia and the Philippines -- played the leading role in organizing the conference and guiding its deliberations. But negotiations on the wording of the ASEAN draft declaration became stuck when China objected to the two key elements in the ASEAN draft proposal.

China, which supports the Pol Pot government Hanoi overthrew, opposed disarming Pol Pot's 30,000-man guerrilla force that is fighting Hanoi's troops. Peking also objected to the establishment of an interim government, which would presumably weaken the claim of Pol Pot forces that they represent the legitimate administration in Cambodia.

As a result, ASEAN was forced to delete any direct reference to an interim government and replace its demand for the disarming of Cambodian combatants with more oblique wording calling for "appropriate arrangements to ensure that armed [Cambodian] factions will not be able to prevent or disrupt the holding of free elections."

T. T. B. Koh, Singapore's U.N. ambassador, said, "In general, we were very pleased with the outcome [because] we managed to preserve the conciliatory nature of the document. It will provide for Vietnam to come into [negotiations] eventually."

European diplomats, however, said the change in wording represents a diplomatic "victory" for China in that "all the crucial words will disappear."

China agreed, however, to drop its objections to a proposal to form an "intergovernmental committee" to consider economic aid to Vietnam "following the peaceful resolution of the [Cambodian] conflict."

ASEAN diplomats attending the conference had hoped, however, to persuade China to soften its line to enable them to preserve the wording of their original draft document, which was designed to provide more clear-cut guarantees to prevent the Peking-backed Pol Pot forces from attempting to forcibly sieze powers should Vietnam remove its troops.

The United States, these diplomats said, shied away from exerting pressure on China. The United States sought a "harmonius" end to the conference, they said, based on an obliquely worded document that would constitute an indirect foreign policy victory for the Reagan administration without putting any new strains on recently more sensitive relations with Peking.

A Western diplomat said the key to the conference was to represent the "clear resolution" of the majority of U.N. members to demonstrate the principle that "Cambodians should have the opportunity to choose their own government free from either external or internal coercion."

The conference declaration, he said, adopted "symbolic measures" by a majority of U.N. members to show that "despite the passage of time, we are not willing to accept what Vietnam is trying to convince us is a fait accompli in the region." He said that there was evidence that Hanoi was beginning to feel the pinch of economic sanctions and political pressure, "but at what point Vietnam decides to change its tactics, I don't know."

Vietnam so far has shown few signs of giving in to that pressure. A commentary broadcast on government-controlled Radio Hanoi today called the U.N.-sponsored conference a "unilateral gathering" constituting "a gross interference in Cambodia's internal affairs."