Iran's President Hassan Rouhani. (Adrees Latif/Reuters)

THE DEADLINE for completing a nuclear agreement with Iran is now less than eight weeks away, and the omens are not good. U.S. officials had hoped that an intensive week of negotiations at the United Nations last month would open the way to a deal but, by the account of both sides, little headway was made. “The gaps are still serious,” said a U.S. official briefing reporters at the end of the talks. Iranian President Hassan Rouhani was even blunter: “The progress realized thus far has not been significant.”

The impasse certainly does not reflect a lack of initiative by the Obama administration. On the contrary, U.S. negotiators have responded to Iranian intransigence on key issues with creative but sometimes disturbing counterproposals. Most notably, Iranian Supreme Leader Ali Khamenei has declared that the regime will not dismantle any of the 19,000 centrifuges it has constructed to enrich uranium. So the United States and its allies, which once insisted that most of the machines be eliminated, reportedly have floated a proposal to leave the centrifuges in place but take away the plumbing that connects them.

If Iran has made similar efforts to bridge the gaps between the two sides, there is no report of them. Instead, Tehran appears to be sticking to its insistence on maintaining and eventually vastly expanding its nuclear infrastructure while offering only a temporary slowdown in uranium enrichment and “increased transparency.” It is refusing to discuss its ballistic missile program and still isn’t cooperating with international inspectors’ probe into its past nuclear weapons design work.

The Obama administration has a history of responding to Iran’s stonewalling by peeling away its own demands. It gave up an attempt to impose a permanent ban on Iranian enrichment and seems to have dropped a requirement that an underground uranium enrichment plant be closed. Now it seems to be contemplating scenarios under which Iran would not have to dismantle centrifuges that would be the center of any bomb-making effort.

In theory, a nuclear deal including this concession could still achieve the goal publicly set by Secretary of State John F. Kerry, which is to increase the time Iran would need to produce a bomb to six months to one year. However, by leaving the nuclear infrastructure intact, it would cede Iran the option of racing to build a nuclear arsenal at a time of its choosing, while removing the sanctions that are pressing the regime. Meanwhile, a concession already made by the United States and its allies — setting a date after which all restrictions on Iran’s nuclear work would lapse — would create a time bomb for the Middle East. Neighbors such as Saudi Arabia would likely take such a date, whether it is five or 15 years away, as a deadline for creating their own capacity for building nuclear weapons.

We have supported negotiations with Iran, and the interim deal struck last year, as preferable to what had previously looked like a slide toward war. But President Obama should resist the temptation to make further concessions in order to complete a long-term deal by November. In the absence of a dramatic change in its positions, Iran should be offered, at best, an extension of the existing arrangement, with the current sanctions left in place — and threatened with tougher measures if it does not accept.