UNITED NATIONS – Arabs, Israelis, and major international powers began thinking yesterday about the day after Yasser Arafat, the one immovable object on the ever-shifting Arab-Israeli scene for nearly four decades.

The visibly ill 75-year-old Mr. Arafat, who has dominated Palestinian Arab politics since the late 1960s, was scheduled to undergo medical treatment in Paris today, leaving his Ramallah headquarters for the first time since Israel confined him there in May 2002.

Although late last night both Arab and Israeli sources shied away from final confirmation of Mr. Arafat’s trip, they were bracing themselves for the possibility of even his temporary absence.

“We are going to continue with the separation plan either way,” Prime Minister Sharon’s spokesman, Raanan Gissin, told The New York Sun, referring to Israel’s unilateral removal of all Jews from Gaza settlements, as well as from four settlements in the West Bank, which passed earlier this week in a historic Knesset vote.

More immediately, Israelis were concerned about nightmare scenarios of unrest in case Mr. Arafat passes away. Military and police forces brought out old “day-after” plans of deployment along possible flashpoints, where grieving Arab crowds might take up arms against Israelis.

“Our biggest nightmare is that, if Arafat dies, a Palestinian mob will come and hustle his body away and try to bury him on the Temple Mount,” an unnamed security source was quoted by Y-net, the Web site of Yediot Ahronot, Israel’s largest circulation daily.

According to other reports, Mr. Arafat and his aides have actually tried to negotiate his burial there with Israel. The site, holy to Muslim and Jews, is known in Arabic as Haram A-Sharif and Israeli authorities were reported to vehemently oppose such a burial.

Mr. Arafat’s trip to Paris was made possible after Prime Minister Sharon, through his adviser Dov Weisglass, assured the Palestinian Arab prime minister, Mahmoud Abbas, that Mr. Arafat would be allowed to leave, and to return afterwards, according to Israel Radio.

Mr. Abbas was said by both Palestinian and Israeli sources to be one of three leaders taking charge of Palestinian Authority affairs in Mr. Arafat’s absence. The other two were Mr. Abbas’s predecessor, Ahmed Qurei, and the head of the Palestinian National Council, Salim Zaanoun.

The men, all in their 70s, are known as “the Tunis generation” of Fatah leaders, a reference to the last residence of Mr. Arafat’s party loyalists before setting up shop in the West Bank and Gaza in the aftermath of the 1993 Oslo Accords. They are unpopular among younger Arabs who grew up under Israeli rule.

“This could end up in chaos, where everybody is against everybody,” a Bar Ilan University professor of political studies, Gerald Steinberg, told the Sun. To solidify power, any of the old men would need the backing of younger Fatah security chiefs, such as Muhammed Dahlan or his nemesis Jibril Rajoub. They would need to fend off any challenge from the Gaza based Islamists of Hamas.

Mr. Steinberg pointed out to the possibility of outside intervention, as in a British initiative that has quietly operated for some months in Ramallah under the title “center for operation.” The center was built to help solidify all security forces under one roof.

The competing security forces structure had been created by Mr. Arafat to assure that none of their commanders ever achieved enough power to overshadow his own. With Mr. Arafat too frail now to exert such power, the British-inspired initiative might succeed now, Mr. Steinberg said.

Last night, a private jet supplied by President Chirac of France was expected to take Mr. Arafat on a journey via Amman, Jordan, to a Paris hospital. Even his wife, Souha, who lives in luxury in Paris, appeared yesterday in Ramallah, where she has not set foot since fleeing in 2000.

Wishing his “warmest wishes for your recovery,” Mr. Chirac wrote a letter to Mr. Arafat, in which he added, “France, as you know, backs the aspiration you embody for the creation of a viable, prosperous and peaceful Palestinian state alongside a state of Israel assured of its security.”

Asked whether the Bush administration wishes the same for Mr. Arafat, State Department spokesman Richard Boucher said, “The gentleman is very ill. This is a matter of seeing that an ill person gets the medical care they need for health.”

Like Mr. Sharon, the Bush administration has considered Mr. Arafat an unfit partner for a negotiated solution. Mr. Sharon’s separation plan, supported by Washington, was envisioned as a unilateral Israeli step. However, “If new opportunities arise, we will reassess the possibility of renewing negotiations” with the Palestinian Arabs, Mr. Gissin told the Sun yesterday.

He explained that Israel has demanded that before any negotiations, the Palestinian Arabs must fulfill steps required by the roadmap, like ending terrorist activities and reforming the government, which was deemed too corrupt under Mr. Arafat.

But Mr. Steinberg said he doubted the separation plan could remain unchanged now. “The premise, that there is no one to talk to, will weaken,” he argued. “Ironically, the settlers now might demand renewal of negotiations with the Palestinians, to assure that Sharon’s plan is delayed.”