The ultra-Orthodox Shas Party, which has 17 members, has also threatened to leave the government.
"Under the current conditions I don't think he can bring back a good deal," said Uli Edelshtein, a member of Sharansky's party in parliament.
Sharansky's party opposes Barak's reported intention to offer the Palestinians at least 85 percent of the West Bank, including the strategic Jordan Valley.
The nationalist and religious right in Israel has begun a major campaign against any peace deal. Former Prime Minister Benjamin Netanyahu voiced opposition Thursday night in his first speech in a year, signaling what could be an effort at a political comeback.
Netanyahu, who edged out Barak in opinion polls last week for the first time since his defeat a year ago, adopted the pose of national healer as he addressed thousands at the West Bank settlement of Ofra.
"In the coming days we may find ourselves facing a bitter argument," Netanyahu said. "It's a dispute between brothers, but there must never be civil war. No Jew must raise a hand against his fellow Jew. Never and under no circumstances."
Even Barak's supposed allies are resisting his latest moves. His foreign minister, David Levy, a former member of the opposition Likud Party, will go to Camp David as part of a 12-man delegation. But Levy has been silent for two days, and he canceled a planned television interview.
Eli Yishai, leader of the 17-member Orthodox Shas Party, part of the Barak coalition, refused to attend the summit.
In the face of such opposition, Barak gave the summit only a 50-50 chance of success.
"It's not possible to assess," Barak said. "Like a toss of a coin."
Still, Barak believes he can bypass his opposition and go to a summit even if he has only 25 percent support in parliament, because he has a mandate from the people and will put any deal to a referendum vote.
"We are at a historic crossroads," he said at a recent graduation ceremony for commando officers. "The first step will be taken next week at Camp David."
Barak has convinced President Clinton that despite wide gaps between the positions of the two sides, the best chance to prevent the region from descending into bloodshed will come through intensive talks with Palestinian leader Yasir Arafat.
"At the original Camp David 22 years ago, more was achieved in 13 days than had been achieved in the previous 13 months," Barak said of the summit that led to a historic peace deal with Egypt. "It took six days before the Americans placed their proposal on the table . . . only on the eighth or ninth day did [then-Israeli Prime Minister] Menachem Begin become convinced that there would be an agreement."
To try to appease his opponents, Barak on Thursday reiterated his "red lines." He said he would never agree to divide Jerusalem, would not allow Palestinian refugees to reclaim homes that are now a part of Israel, and would not abandon the nearly 200,000 Jewish settlers in the West Bank and Gaza Strip, two areas that Israel occupied in the 1967 Six-Day War.
There are significant conflicts between Barak's public positions and those of Arafat, who demands that Israel withdraw fully from the West Bank and dismantle all settlements. Arafat also insists that East Jerusalem become the capital of a Palestinian state.
Barak's own aides were reported Thursday to have said that no matter the outcome of the summit, the government, as currently constituted, is in its death throes. If the summit produces a deal, Barak may consent to early elections, possibly combined with a referendum on the peace agreement. If he has correctly read the public support for such a deal, the electorate might give him a fresh mandate.
If the peace talks fail, Barak may join forces with the hawkish Likud Party, forming a government of national unity in hopes of buying domestic peace and steeling the nation for the possibility of a violent confrontation with the Palestinians.
"Barak has reached the summit of his desires preoccupied by intrigues and plucked of his feathers, with his coalition walking a very thin wire and his public standing at a low point," wrote Hemi Shalev of the Israeli newspaper Maariv. "In order to achieve an agreement he will have to give up basic and important assets, and then convince the public that it is worthwhile doing so."
Still, the prime minister is convinced that whatever his own ratings in the polls, there is overwhelming public support for a peace deal that would end a half-century conflict with the Palestinians. That, and his own conviction that the timing and confluence of events will never be better for a peace deal, have stiffened his resolve in the face of broad skepticism.
Nomi Morris' e-mail address is nmorris