The Bush administration is beginning a flurry of diplomatic activity aimed at ending Cambodia's long civil war and resolving other matters left over from the Indochina conflict.

State Department officials described to a House subcommittee Wednesday new efforts to persuade Vietnam and other critics to accept the Cambodian peace formula backed by the five permanent members of the U.N. Security Council.The scene shifted Thursday to the Senate Foreign Relations Committee, where Democrats have voiced impatience over the continuing bloodshed in Cambodia and lingering problems with Vietnam.

Unfinished business from the 1970s includes settling the status of about 1,700 American servicemen still unaccounted for in Indochina, and normalizing trade and credit with Vietnam, needed by Hanoi to replace economic help formerly provided by the Soviet Union and East European countries.

Assistant Secretary of State Richard Solomon told the House Asia-Pacific subcommittee that the Cambodian plan backed by the United States, Soviet Union, Britain, France and China provides the best guarantee against a return to power by Cambodia's communist Khmer Rouge.

The Khmer Rouge are blamed for at least a million deaths during their 1975-78 rule over Cambodia. They are the strongest of three guerrilla forces battling the Vietnamese-installed government in Phnom Penh.

Many in Congress as well as Hanoi contend including the Khmer Rouge in the peace process risks returning them to power.

But Solomon said Wednesday, "The only way the Khmer Rouge can win is if the settlement process is blocked and the military struggle continues." He added that China, once the main supplier, claims it cut off shipments to the Khmer Rouge last year because of progress toward a settlement but has threatened to resume if others faction get arms.

Solomon also said he has the impression China and the Soviet Union have reached an understanding to try to achieve peace in Cambodia.

The settlement formula provides for choosing Cambodia's future government in free elections prepared by "a very aggressive" United Nations peacekeeping force after demobilizing all guerrilla and regular military forces in the country, Solomon said.