The United States appealed yesterday for international humanitarian efforts to forestall a disastrous famine in Cambodia.

A State Department announcement by spokesman Thomas Reston deplored efforts by rival regimes in war-torn Cambodia to gain "political advantage" from relief efforts. No group that impedes the flow of emergency relief can lay claim to representing the aspirations of the Cambodian people, the statement declared.

The United States is barred by law from aiding Cambodia, but State Department lawyers believe there may be a loophole for humanitarian assistance. Consultations about the law have been held with members of Congress, some of whom have been urging vigorous U.S. action to stave off a famine.

The United States stands ready to contribute "within the limits of U.S. law to an international relief effort" under international supervision aimed at aiding all Cambodians, the State Department said.

The statement reiterated a plea made by Secretary of State Cyrus R. Vance to Asian foreign ministers in early July and to Congress in late July. Officials said the U.S. appeal was repeated because of increasingly grim reports of food shortages.

Most of Cambodia is under the control of a Vietnamese-backed regime installed after Hanoi's invasion last Dec. 25. However, the Chinese-backed Pol Pot insurgents are still holding out in remote areas and carrying on daily battles against the Vietnamese.

Efforts by the United Nations, the International Red Cross and several neutral governments to provide food and relief supplies inside Cambodia have been unsuccessful. Each Cambodian regime has attached conditions to the distribution of aid, in an effort to make sure no food or supplies reach the hands of its enemies.

The State Department statement yesterday did not repeat the U.S. call for a political conference to forge a political solution to the Cambodian conflict. Such a negotiated solution is considered remote at present.

American diplomats have held talks at the United Nations and elsewhere to urge an international relief program that could cut through the political and military conflicts to reach the Cambodian people. One suggestion made by Vance was an international committee including representatives of opposing international groups - in this case, both Soviet-aligned and Chinese-aligned nations - to administer a Cambodian food program.

The State Department statement said the United States has contributed $300,000 to the International Committee of the Red Cross to help Cambodian refugees in Thailand, and $325,000 to a private voluntary agency to provide food in the Thai-Cambodian border area.

The international efforts could be directed at all Cambodian people "irrespective of their location or the political authority under whose control they fall," the statement said.