Prince Norodom Sihanouk, the former ruler of Cambodia now in rebellion, and Premier Hun Sen, the leader of its Vietnam-supported government, signed an agreement Friday that could lead to a negotiated end of the long civil war in their country.

Much depends on whether the Khmer Rouge, the powerful partner in Prince Sihanouk’s rebel coalition, will heed the call of Sihanouk and Hun Sen to join them in future negotiations.

The agreement, signed with great ceremony before television cameras, does little more than set the ground rules for future negotiations. But there was an optimistic air in the secluded chateau in Fere-en-Tardenois, 75 miles east of Paris, where the 65-year-old Sihanouk and the 36-year-old Hun Sen signed the document after meeting over the last three days.

Handshakes and Toasts

The two Cambodian foes shook hands, embraced and toasted each other and Cambodia with champagne as Sihanouk predicted to journalists that he would be back in Cambodia by 1988 or, at the latest, 1989.

Sihanouk, the traditional ruler of Cambodia who has served as head of state for various factions in the past, said that everyone in Cambodia wants peace but that “a peace without 100% independence was not acceptable.” This was an obvious reference to Vietnam, which now props up the Hun Sen government by keeping 140,000 troops in Cambodia.

There were signs, however, that the Vietnamese, wearied by years of rebellion, fully back the negotiations. Vietnam’s Communist Party newspaper, in an editorial Thursday, described the talks in France as “a breakthrough in the eight-year-old stalemate.” Also, the Vietnamese government announced some time ago that it intended to withdraw all of its troops by 1990.

Sihanouk also made it clear that any future political system of Cambodia would have to absorb the Khmer Rouge in some way. In their three years in power, the Khmer Rouge, headed by Pol Pot, ran one of the most tyrannical and murderous regimes in world history. Their atrocities provided the Vietnamese with an excuse for invading Cambodia at the end of 1978.

The Khmer Rouge now make up two-thirds of the Sihanouk coalition’s rebel force of 60,000, and Sihanouk implied that he believed they would be no threat if they returned to Phnom Penh as a minority element in a democratic, French-style, multiparty political system. Likening the Khmer Rouge to Jean Marie Le Pen, the extreme rightist leader in France, Sihanouk said, “It would not matter if there were a Khmer Le Pen.”

Hun Sen described the agreement as “the victory of the policy of national reconciliation of Prince Norodom Sihanouk and also that of the national policy of reconciliation of the Popular Republic of Kampuchea,” as Hun Sen’s Cambodian government is known.

January Talks Planned

The premier and the prince said they will meet again in January in Fere-en-Tardenois, a favorite retreat of Sihanouk’s. A third round of talks will be held in Sihanouk’s residence in Pyongyang, North Korea, but no date was set.

The agreement comprised four simple points. First, it stated that only “a political solution” could settle the Cambodian conflict--a tacit acknowledgment by both sides that a military victory was not possible.

The second point states that only the Cambodian people can settle the conflict through “negotiations among all sides of the conflict.” This seems to put the Vietnamese, at least in any formal way, outside the peace process, and to include the Khmer Rouge instead.

In their third point, Sihanouk and Hun Sen agreed that once all Cambodian parties had reached an accord, an international conference would be called to guarantee both the accord and the independence of Cambodia.

Finally, the two Cambodians set the date for the next round of talks and promised that there would be a third round as well.