It took nine years, the collapse of communism in Eastern Europe and exhaustive diplomatic bargaining, but finally a United Nations peace plan has been agreed upon for Cambodia. It accomplishes the essential goals of verifying the withdrawal of all Vietnamese occupation troops and ensuring a free and fair election of a new government under U.N. supervision but at a very high cost.

This high price is not the $5 billion needed for a U.N. force, a sum that will invariably be halved; it is letting the Khmer Rouge off the hook to achieve international consensus. Pol Pot and his followers are being accorded the same rights and privileges as all other Cambodians, with immediate and far-reaching consequences. They put Son Sen, the man who had authority over Pol Pot's Gestapo-like security system, on a new interim council for Cambodia. They will be free to campaign during elections with huge campaign funds from China -- the essence of this bargain for peace.

Fortunately, the U.N. peace plan is so elastic the damage can be limited, especially if countries such as the United States act now. At a minimum, Congress could add on humanitarian aid for the people inside Cambodia to the Solarz aid package for the Cambodian noncommunist resistance. If the United States gave this aid through international organizations and posted an American diplomat in Phnom Penh now to oversee that aid, all the better. This would demonstrate America's commitment to its oft-spoken pledge not to allow the Khmer Rouge back in power.

For the war continues. The Khmer Rouge have not stopped their terrorist attacks, and they are trying to choke supply routes, with the tragic result that once again in Cambodia food and medical supplies are running short. Until a peace treaty is actually signed, there is no cease-fire in Cambodia and no date for holding elections. Peace may be tantalizingly near, but so, too, are the Khmer Rouge, with their midnight massacres of village chieftains and their threats to undermine the peace process.

The United States is not solely responsible for this peace plan. It is important that individuals as diverse as Soviet leader Mikhail Gorbachev, French diplomat Claude Martin, U.S. congressman Stephen Solarz, Australian foreign minister Gareth Evans, Thai prime minister Chatichai Choonhaven and U.S. Secretary of State James A. Baker III all played pivotal roles to bring about peace. But in the end, the final U.N. framework is nearly identical to one designed at a 1981 conference on Cambodia that calls for the withdrawal of foreign forces, a cease-fire, free elections under the U.N. and all within a ''comprehensive political settlement.'' In other words, the bargain was struck nine years ago to uphold international laws forbidding foreign occupation and to ignore laws forbidding gross human rights abuses and genocide -- to win peace by including rather than excluding the Khmer Rouge.

That is now history. The issue today is how to ensure that the consequence of this peace is not another war, to borrow a phrase from John Maynard Keynes. Someday there may be a trial and everyone from Pol Pot to Hun Sen to Prince Norodom Sihanouk could be judged for their roles in the Cambodian tragedy. Today, all the nations that have worked so hard to craft this framework should show up in force inside Cambodia, now, before final treaty signatures, and not only give aid but show with their presence that stalling tactics won't work and that this peace is not a prelude to another war. The writer, a special correspondent for The Post, is the author of "When the War Was Over: A History of the Cambodian Revolution."