RAMALLAH, West Bank — Less than two weeks before Palestinians plan to defy the Obama administration by requesting membership and statehood recognition at the United Nations, there is a growing fear that the Arab-Israeli conflict is entering an explosive new phase.

A Palestinian decision to shift its statehood quest toward international legal and political pressure on Israel, combined with Israeli fear and truculence at a time of regional upheaval, has many predicting disaster, especially after the storming of Israel’s Cairo embassy and the expulsion of its ambassador from Turkey.

“Israel is already facing hostility from Egypt, Turkey and Gaza,” a senior Western diplomat said. “It will react to a Palestinian statehood bid with punitive measures in the West Bank. Congress will probably cut off aid to the Palestinians. The Palestinian Authority could collapse. We’re watching a potential train wreck.”

In response, Palestinians say that their lives have long been a train wreck — an Israeli-induced one of settlement and occupation — and that it is time for a radical shift in approach. They say their United Nations effort, along with accession to international legal forums, will be followed by renewed negotiations with clearer guidelines. The Israelis say the move will kill the chance of future talks.

In fact, no one knows where it could lead. The details of the United Nations membership bid are still being worked out — on Monday, the Palestinian president, Mahmoud Abbas, is due in Cairo to present his plan to the Arab League — and some of what is happening is brinkmanship. But on the ground there are ominous hints. The Israeli Army is holding dress rehearsals for Palestinian riots. Radical settlers vandalized mosques and an Israeli military base last week.

Meanwhile, a complex set of diplomatic endeavors is under way to slow down or at least shape the United Nations process. There is little optimism accompanying the effort.

Tony Blair, the former British prime minister who represents the Quartet — the diplomatic group focused on the Middle East that is made up of the United States, European Union, United Nations and Russia — is looking for a new basis for Israeli-Palestinian negotiations. He hopes that a Quartet statement will cushion or shift the membership bid toward talks. The Israelis are grateful, the Palestinians annoyed. Officials from most other countries are skeptical.

American diplomats were here last week warning Mr. Abbas of unforeseen consequences from his statehood bid. Having the power to take Israeli officials to the International Criminal Court may sound appealing, they said, but it will not end the occupation and is likely to make it worse. If the Palestinian Authority falters, Hamas will fill the vacuum, they said, adding that the only way forward is direct negotiation.

“Americans want to preserve the existing paradigm,” a diplomat from another country said. “But many are saying to them: ‘You are living in the last century. Nothing has happened in that paradigm. It’s time to move on.’ ”

Prominent among those voices are the French, whose officials, including President Nicolas Sarkozy, have privately said that the Oslo peace process, begun in the Norwegian capital in 1993 and the framework for Israeli-Palestinian interactions since, has run its course. It is time, they say, for state-to-state negotiations between Israel and a prospective Palestine.

French diplomats are trying to help the Palestinians shape a United Nations resolution that describes statehood on the 1967 lines, along with agreed land swaps with Israel, but slows down bilateral recognition between a Palestinian state and other nations. This is partly aimed at luring the Germans, who are unenthusiastic. Europeans say they believe that their unity in this issue is important.

Israel is horrified. To abandon Oslo, its leaders say, is to destroy any hope of negotiations, because that will rip up the legal basis for talks. If a United Nations resolution defines Palestine as within the 1967 lines, that means 500,000 Israelis will be defined as occupiers in another country. To pre-empt that, there are suggestions here to annex certain areas first or withdraw travel privileges for Palestinian officials in the West Bank.

“If the Palestinians go to the United Nations, it will begin a long funeral for the peace process and negotiations,” Yuli Edelstein, Israel’s minister for public diplomacy, told a group of visitors in Tel Aviv on Thursday night.

There are two routes that Mr. Abbas is considering at the United Nations. His preference is to begin by applying through the 15-member Security Council for full membership. The United States has vowed to use its veto there.

If that failed, he could then go directly to the 193-member General Assembly, where there is no veto and a pro-Palestinian majority. The General Assembly cannot grant United Nations membership to Palestine, however. It can only declare it to be an observer state. But the key word is “state,” because that would allow it to join a host of international agencies and treaty groups, including the International Criminal Court, the International Court of Justice, Unesco and others.

“The title ‘state’ will open so many doors to us,” said Ammar Hijazi, a Palestinian official who has done much of the background work on the United Nations application.

But full membership through the Security Council would bring greater stature and more obligations from fellow member states. The Palestinians say that while they are not looking for a confrontation with Washington, that is the route they want.

If they take it, a committee of all 15 members of the Council will be set up to study the application. That process could take a day or a month. The United States committee member could request a delay, giving Mr. Blair and others time to come up with a new formula for negotiations.

If the Palestinians go directly to the General Assembly, they are likely to submit the application around Sept. 20 and seek a vote a couple of weeks later. Once admitted — a foregone conclusion — Palestine would join all international legal forums.

The Palestinians have been seeking admission to the International Criminal Court in The Hague for nearly two years, and the chief prosecutor, Luis Moreno-Ocampo, has indicated that General Assembly acceptance would make the difference.

Palestinians would then be entitled to bring cases against Israeli officials, perhaps for actions related to building West Bank settlements viewed as illegal. This issue worries the Israelis perhaps most of all.

But others say that the Palestinians should also worry. Statehood and membership in international courts would bring obligations they might not be able to meet. A rocket from Gaza would be cause to bring them to account, for example.

Moreover, if the Palestinian Authority ended up withering for lack of support and security cooperation with Israel, Hamas would be waiting in the wings. A Hamas takeover attempt in the West Bank is not something Israel would accept lightly, and the army would most likely turn its attention from riot control to something far more lethal.

Even some relatively liberal Israeli politicians have expressed unhappiness with Mr. Abbas’s plans.

“He knows he is not getting a state,” said Einat Wilf, an Israeli member of Parliament. “He knows he is not resolving anything. He is simply taking the conflict to another place.”

The Palestinians, Ms. Wilf said, “will take each and every body of the U.N. and use it as a theater to continue this whole conflict.”