WASHINGTON (JTA) — Vast majorities in the U.S. House of Representatives and the U.S. Senate signed letters to President Obama urging congressional oversight of nuclear talks with Iran and outlining congressional expectations of a deal.

The letters sent Tuesday were backed by the American Israel Public Affairs Committee and signed by 83 of 100 senators and 394 of 435 House members.

Each outlines expectations for any final deal to emerge from the talks underway now between Iran and the major powers, led by the United States.

The letters differ, however, in tone, with the Senate letter more definitively describing outcomes that “must” be in place and the House letter instead saying its signatories were “hopeful” of such outcomes.

“Any agreement must dismantle Iran’s nuclear weapons program and prevent it from ever having a uranium or plutonium path to a nuclear bomb,” the Senate letter said.

“We are hopeful a permanent diplomatic agreement will require dismantlement of Iran’s nuclear weapons-related infrastructure, including enrichment-, heavy water-, and reprocessing-related facilities, such that Iran will not be able to develop, build, or acquire a nuclear weapon.

The letters, initiated by Sens. Robert Menendez (D-N.J.), the chairman of the Senate Foreign Relations Committee, and Lindsey Graham (R-S.C.), and Rep. Eric Cantor (R-Va.), the House majority leader, and Rep. Steny Hoyer (D-Md.), the House minority whip, were a key focus of AIPAC’s lobbying day culminating its annual conference earlier this month.

The Senate letter suggests that the body could soon reconsider new sanctions on Iran, a bid also backed by AIPAC that the Obama administration deflected earlier this year.

“Should negotiations fail or Iran violate the Joint Plan of Action, Congress will need to ensure that the legislative authority exists to rapidly and dramatically expand sanctions,” the letter said.

The Joint Plan of Action is the agreement that led to the interim talks.

“We must signal unequivocally to Iran that rejecting negotiations and continuing its nuclear weapon program will lead to much more dramatic sanctions, including further limitations on Iran’s exports of crude oil and petroleum products,” the Senate letter said.

“AIPAC applauds this overwhelming demonstration by the U.S. Senate of its determination to prevent Iran from achieving nuclear weapons capability,” the organization said in a statement. The lobby also praised the House letter in a separate statement. “AIPAC appreciates the strong message sent by the House showing America’s determination to prevent Iran from achieving a nuclear weapons capability,” it said.

Sen. Carl Levin (D-Mich.), the chairman of the Senate’s Armed Forces Committee, launched a separate letter that copied the language of a the Cantor-Hoyer House letter.

Levin did not say why he preferred the Cantor-Hoyer letter, but that letter was closer to the position of the Obama administration, explicitly saying that its signatories “do not seek to deny Iran a peaceful nuclear program.”

Israeli Prime Minister Benjamin Netanyahu and a number of Republicans in Congress say that any deal must end uranium enrichment altogether; Obama administration officials have said that a limited degree of enrichment is the likely outcome of any deal. The Menendez-Graham letter does not explicitly count out an enrichment capability for Iran.

Levin had not yet sent his letter, although lobbyists backing it say that over 20 senators had signed it, meaning that there are senators who have signed both letters.

The liberal Jewish groups Americans for Peace Now and J Street backed the Cantor-Hoyer letter in the House and the Levin letter in the Senate.

Americans for Peace Now opposed the Menendez-Graham letter in the Senate, and J Street had no position on it.

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