“A showdown in New York could have adverse negative consequences for the Palestinian people and for our partners and allies at a time when things are already fragile,” Rice said at a Christian Science Monitor breakfast in Washington. Rather, she said, Israelis and Palestinians must come together for peace talks.

Mahmoud Abbas, president of the Palestinian National Authority, is set to deliver a formal request on Sept. 20 for the U.N. General Assembly to approve statehood for Palestine, as world leaders including President Barack Obama gather in New York.

If there is a vote, Rice said, the effect on Palestinian “relations with the United States is for the president and the Congress to decide.”

Rice said that “steps to try to circumvent” peace talks, such as a U.N. vote on statehood, “are ultimately counterproductive and self-defeating.”

If there is a vote approving Palestinian statehood, “This isn’t one day of hoo-ha and celebration … and then everybody goes home,” Rice said.

Countries that would vote for Palestinian statehood would “have a responsibility to own the consequences of their vote,” she said. A U.N. resolution wouldn’t create borders, improve the economy or otherwise set Palestinians on a path to true statehood.

The Obama administration has mounted an intense campaign in recent days to head off the Palestinian initiative. U.S. Middle East peace envoy David Hale and National Security Council adviser Dennis Ross met with Abbas in Ramallah last week, urging him to ditch the effort. In addition, the U.S. has been working with its three partners in the so-called quartet — the European Union, Russia and the U.N. — to craft an alternative proposal to restart peace talks.

There would be “real-world implications” of a U.N. statehood vote, Rice said, and U.S. diplomats are having “very plain discussions” about the potential fallout with countries — including a majority of General Assembly members — that are seen as favoring the Palestinian resolution.

The U.S. has pledged to veto a statehood measure in the U.N. Security Council. However, the U.S. lacks any official power to prevent the broader General Assembly from upgrading the Palestinian delegation from its current status as a nonvoting observer “entity” to a nonvoting observer “state.” With that enhanced status, the Palestinians could take some actions against Israel, including filing cases in the International Criminal Court.

Rice also spoke about the latest round of calls coming largely from Republican members of Congress for the U.S. to diminish its role in the U.N.

“Long before we were talking about action at the United Nations by the Palestinians, there have been those in Congress who have viewed the United Nations with some skepticism, let’s say,” she said. But the Obama administration has “consistently” opposed those efforts “because they are self-defeating and they consistently don’t work,” she said, pointing to efforts in the 1980s and 1990s.

Legislation reducing U.S. financial contributions to the U.N. would harm efforts for Rice and her team to change the body from within, she said. It is better for the U.S. to seek transparency and greater fiscal responsibility, among other reforms, as a responsible and paying member “than as a laggard and a debtor who is carping from the outside” about the need for reform, Rice said.

Meanwhile, diplomats are warning that any attempt by the U.S. to block or undermine the Palestinian bid could lead to a “toxic” reaction in the Arab world. “American support for Palestinian statehood is, therefore, crucial, and a veto will have profound negative consequences,” Prince Turki al-Faisal, a former Saudi ambassador to the U.S., wrote in a New York Times op-ed Monday.

The faceoff over Palestinian statehood at the U.N. comes as Israel is facing increasing isolation on the diplomatic front. Relations with Egypt and Turkey — two of the few majority-Muslim nations that recognize Israel — have soured in recent months.

Last week, protesters stormed the Israeli Embassy in Cairo, stoking Israelis’ fears that the Arab Spring democracy movement has unleashed popular hostility toward the Jewish state. Under pressure from the Obama administration, the Egyptian government moved somewhat belatedly to quell the protest and safeguard the embassy. However, after the violence, Israel decided to evacuate its ambassador and the rest of the embassy staff.

Egyptian officials blamed outside agitators for fomenting the embassy violence. The protests followed a series of cross-border attacks and clashes, in which eight Israelis, five Egyptian soldiers and about 10 militants died.

Israel’s once-close relationship with Turkey has become increasingly chilly, particularly after the release of a U.N. report this month on the military raid Israel mounted in 2010 against a Turkish flotilla carrying aid and anti-Israel activists to Gaza in defiance of a blockade Israel had imposed. The U.N. report found that the blockade was legal but that the use of force was “excessive and unreasonable.”

Both Turkey and Israel have publicly disputed the report’s findings. Turkey also expelled Israel’s ambassador in Ankara.