Another Step Toward Nuclear Sanity in Iran If all goes according to plan, Iran will begin freezing and then rolling back its most worrisome nuclear activities on Monday under an agreement reached over the weekend with the United States and other major powers. This would be the most significant restraint ever on a program that has threatened international stability since it was first disclosed in 2002 and an undeniably important step toward the peaceful resolution of a serious dispute. Even so, dangerously misguided forces, including leading Democrats and Republicans in Congress, are working to sabotage it. The broad outlines of the deal, to be replaced in six months by a more permanent one, were reached in November. Now the major powers and Iran have settled on detailed procedures for making it work. Iran has agreed to stop enriching uranium beyond 5 percent, a level sufficient for energy production but not enough to fuel a bomb. Its stockpile of uranium enriched to 20 percent - a level alarmingly close to weapons-grade fuel - will be diluted or converted to a less threatening substance. Iran also agreed not to install new centrifuges, start up any that were not already operating or build new enrichment facilities. It will allow inspectors from the International Atomic Energy Agency to have unprecedented, in some cases daily, access to some sites. Once the agency confirms that Iran has begun to take the promised actions, the major powers will suspend certain sanctions so Iran can resume petrochemical exports, trade in gold and other precious metals, and imports of spare parts, especially for airplanes. The major powers will stop pressuring other countries to reduce oil imports from Iran and will facilitate humanitarian trade, making it easier for Iran to obtain needed medicines and make tuition payments for Iranian students abroad. Iranian funds frozen in foreign banks amounting to $4.2 billion will be released in increments, beginning with a $550 million payment in February. The most crippling sanctions will remain in force until a permanent agreement is in place. These sanctions have severely constrained Iran's oil exports, foreign investment in Iran's energy industry and Iran's ability to engage in international financial transactions. American officials have made clear that if Iran cheats, any sanctions that had been eased would be reimposed and tougher ones enacted. Nevertheless, these commitments have not dissuaded lawmakers like Senator Robert Menendez, a Democrat from New Jersey and the chairman of the Senate Foreign Relations Committee, and Senator Mark Kirk, a Republican from Illinois, from pushing legislation that would impose new sanctions. This would violate the interim agreement and set unworkable conditions for a final deal. Israel's government and pro-Israel interest groups are pressing the same hard line. President Obama has threatened to veto such a bill if it passes. But it would be far better if the critics, especially members of his own party like Mr. Menendez, came to their senses. There are no guarantees that the next six months will produce a final deal that permanently restrains Iran from a nuclear weapon, but the interim deal at least offers hope for one. Conversely, if negotiations fail - which would surely happen if Congress ties Mr. Obama's hands - Iran is likely to embark on an even more aggressive search for a nuclear weapon. And that could leave war as the only option.