Tehran, Iran ? Iran said Tuesday it was ready for “serious negotiations” on its nuclear program, offering a new formula to resolve a crisis with the West. A semiofficial news agency said the government was unwilling to abandon uranium enrichment – the key U.S. demand.

Iran delivered its written response to a package of incentives offered by the United States and five other world powers to persuade Iran to roll back on its nuclear program – and punishments if it does not. The world powers, the five permanent U.N. Security Council members plus Germany, have given Iran until Aug. 31 to accept the package.

The U.S. ambassador to the United Nations, John Bolton, said Washington will “study the Iranian response carefully” but was prepared to move forward with sanctions against Tehran if it was not positive. The White House held off commenting until it had studied the text. The European Union’s foreign policy chief, Javier Solana, said the document was “extensive” and required “a detailed and careful analysis.”

Iranian officials offered no details of the response, but it appeared geared at enticing those countries into further negotiations by offering a broad set of proposals vague enough to hold out hope of progress in resolving the standoff.

If the Iranians leave the door open to halting enrichment as talks progress, that would drive a wedge in the Security Council between the Americans, British and French on one side and the Russians and Chinese on the other. Last month, Russia said the Council was in no rush to pressure Iran, striking a more conciliatory tone than the United States.

Today, China also appealed for dialogue to settle the dispute over Iran’s nuclear program, urging the parties involved to “remain calm and patient, show flexibility, stick to the orientation of peaceful resolution and create favorable conditions for resuming talks as soon as possible.”

Tuesday’s announcement was the latest development in the yearlong standoff over Tehran’s nuclear program. Iran says it wants to master the technology to generate nuclear power. But critics say Iran is interested in uranium enrichment because it can also be used to make the fissile core of nuclear weapons.

The current drama is playing out in the wake of fears that the ability of the pro-Iranian Hezbollah guerrillas in Lebanon to withstand 34 days of Israeli bombardment has emboldened hard-liners in Tehran to risk a showdown with the Americans, who are bogged down in neighboring Iraq. There also has been speculation in the West that Iran encouraged Hezbollah to provoke the Israelis to distract attention from its nuclear ambitions.

Iran has pursued a confrontational stance on the nuclear issue since the election of President Mahmoud Ahmadinejad last year. The hard-line president has used the nuclear issue to encourage a sense of national pride.