Bush administration officials say Iran should be given time to consider a package of incentives, aimed at halting the country's nuclear enrichment and reprocessing activities.
White House spokesman Tony Snow says Tehran will need some time to mull over the offer, and the first response may not be the last word.
"I would caution against leaping to conclusions, until the leadership in Iran has actually had an opportunity to look over the packages of incentives and disincentives offered by the EU-3 with the support of the United States," he said.
The plan was drafted by the three European nations that have been negotiating the nuclear issue with Iran - Britain, France and Germany - with the backing of the United States, Russia and China. Details of the package have not been formally released.
During a session with reporters, Snow downplayed comments over the weekend by Iran's supreme leader, Ayatollah Ali Khamenei, who said the flow of Iranian oil will be disrupted if the United States makes - what he called - a wrong move.
The White House spokesman predicted there will be a number of statements coming out of Iran before Tehran gives its final answer. He said, at the moment, the White House is neither optimistic nor pessimistic, but hopeful.
"It is easy to make comments into a vacuum, and my sense is that, again, the Iranians are going to realize this is a serious offer, and it is an offer that offers great promise for them," Snow said.
European Union foreign policy chief Javier Solana is to formally present the package to the Iranian government in Tehran, perhaps as early as Tuesday.
Last week, U.S. Secretary of State Condoleezza Rice urged Iran to give careful consideration to the plan, but indicated Tehran would not have an indefinite amount of time to respond.
Iranian officials have indicated they plan to study the document, but stress they have no plans to suspend uranium enrichment, a key condition that has been attached to the deal.
Tehran says it is processing uranium for use in power plants. But the United States and Europe say they are concerned Iran's civilian nuclear power program is really a cover for the development of nuclear weapons.