President Barack Obama hailed Saturday’s interim agreement with Iran as a major step toward halting that nation’s pursuit of a nuclear arsenal. But unfortunately, his words of reassurance can’t alter the chilling reality that under this accord, Iran has considerable leeway to keep advancing its longtime nuclear ambitions

The United States, joining with Britain, Russia, China, Germany and France, signed that deal with Iran in Geneva.

President Obama called it “an important first step,” contending: “These are substantial limitations which will help prevent Iran from building a nuclear weapon. Simply put, they cut off Iran’s most likely paths to a bomb.”

The accord, which eases economic sanctions on Iran, focuses on international inspections to verify that it is not enriching uranium to levels needed to make nuclear weapons. The agreement also imposes a temporary shutdown of a research reactor whose byproduct is plutonium, a potent nuclear arms material.

Yet the Islamic republic will have the ability to brush aside long-term international controls. That’s a serious threat to Israel and Saudi Arabia. Officials of both nations have denounced the interim agreement.

So have numerous U.S. lawmakers on both sides of the aisle.

As New York’s Charles Schumer, the No. 3 Democrat in the Senate, put it in a statement released Sunday: “This disproportionality of this agreement makes it more likely that Democrats and Republicans will join together and pass additional sanctions when we return in December.”

Sen. Schumer added: “It was strong sanctions, not the goodness of the hearts of the Iranian leaders, that brought Iran to the table, and any reduction relieves the psychological pressure of future sanctions and gives them hope that they will be able to gain nuclear weapon capability while further sanctions are reduced. A fairer agreement would have coupled a reduction in sanctions with a proportionate reduction in Iranian nuclear capability.”

And Iran is sticking to its claim, uncontested in the interim agreement, that it has the right to control its “nuclear fuel cycle” — starting with the right to manufacture uranium fuel for peaceful nuclear reactors.

Iran already has produced fuel rods for its first nuclear power reactor at Bushehr and is planning to build more nuclear power plants.

Meanwhile, it’s dangerous folly to assume that the international community will quickly — if ever — agree to reimposing tough sanctions on Iran if it persists in its nuclear ambitions.

President Obama apparently let his zeal to reach an agreement with Iran cloud his judgment.

He should have heeded the wisdom of a White House predecessor who engaged in successful arms control negotiations of his own.

As recounted in last Thursday’s Wall Street Journal by George Schultz, who served Ronald Reagan as Secretary of State, his boss had instructive views on negotiation strategy, concluding with this astute observation:

“The guy who is anxious for a deal will get his head handed to him.”

And the deal that Secretary Kerry and President Obama have handed to Iran’s mullah leaders give them a virtually clear field to continue their march toward nuclear weapons, though perhaps at a slower pace.

So who is going to stop Iran from extracting plutonium from used uranium fuel rods when the opportunity presents itself a few years from now, just as North Korea has done?

The interim agreement may buy a few months of relaxed tensions — except in Israel and Saudi Arabia.

But it doesn’t really ease the threat of a nuclear-armed Iran.

Instead, it sustains that menace.