PARIS, JAN. 20 -- Prince Norodom Sihanouk, the Cambodian rebel leader, opened a second round of peace talks with Prime Minister Hun Sen today, discussing a timetable for Vietnamese troops to withdraw from the country as part of a regional agreement.

The talks, at a hotel in the Paris suburb St. Germain-en-Laye, resumed after a six-week pause in an atmosphere of increased expectation that a settlement might eventually be possible among Cambodia's warring parties and the larger powers that support factions in the war-scarred nation.

Gaston Sigur, the U.S. assistant secretary of state for Asia and the Pacific, said Monday in Bangkok that there are new signs that Vietnam is seeking a political solution to the conflict. Similarly, an Asian diplomat said chances for a Cambodian settlement have improved because of the recent relaxation in U.S.-Soviet relations.

Hun Sen, briefing reporters after today's talks, said negotiators debated conditions and dates for withdrawal of the 140,000 Vietnamese troops who have supported his government in Phnom Penh since toppling the bloody Khmer Rouge regime and occupying the country in 1978. He declined to give details but told reporters the withdrawal would have to be linked to disbanding the Khmer Rouge guerrillas.

Sihanouk's son, Prince Ranariddh, announced that his father and Hun Sen will continue their talks here Thursday. The two also have agreed to meet again in the spring in North Korea, where Sihanouk has a residence, then in France and later in India, he said.

Natwar Singh, the Indian minister of state for foreign affairs, met here this week with Cambodian government and rebel leaders in anticipation of this round of talks. A high-ranking Indian diplomat expressed hope recently that the negotiations could lead to an international conference in New Delhi later this year to organize regional guarantees for any peace accord.

Sihanouk, the former Cambodian monarch who heads a rebel coalition backed by China and the United States, made no comment.

Sihanouk and Hun Sen agreed in principle after three days of talks Dec. 2-4 in the French town Fere-en-Tardenois that Cambodia's years of warfare should be settled politically. The December talks were the first among Cambodia's warring factions.

In a communique issued then, Hun Sen and Sihanouk also declared the conflict should be resolved primarily among Cambodians, meaning between the Hun Sen government sponsored by Vietnam, and the rebel coalition including Khmer Rouge guerrillas.

Observers pointed out, however, that the chances for success depend equally on Vietnam, which keeps Hun Sen's government in place, and China, the main regional power that supports the rebel coalition and, in particular, the Khmer Rouge and its infamous leader Pol Pot. Sihanouk thus has sought a peace formula that would be acceptable to Vietnam and China.

The Khmer Rouge have denounced Sihanouk's efforts and refused to abide by them. This means China likely would have to drop its main Cambodian ally or persuade it to abandon years of warfare to support any agreement between Hun Sen and Sihanouk.

The Khmer Rouge is the largest fighting force in the guerrilla coalition headed by Sihanouk. With this in mind, Vietnamese officials have expressed reluctance to withdraw their forces without guarantees to prevent Pol Pot's group from threatening a renewal of its three-year reign of terror.