Washington ? President Bush has decided to offer modest economic incentives to Iran in exchange for Tehran’s abandoning its nuclear enrichment program, two senior administration officials said Thursday.

As recommended by the European leaders who have been negotiating with Iran, the incentives include possible membership for Iran in the World Trade Organization and the sale of commercial aircraft parts to Tehran.

In exchange for offering incentives, the United States obtained a firm agreement from Britain, France and Germany to refer the matter to the U.N. Security Council for sanctions if Iran does not permanently drop its nuclear program, the two officials said. They spoke on condition of anonymity.

The United States agreed not to oppose talks on WTO membership for Iran — a process that normally takes years — and to permit the aircraft part sales, they said. The part sales would be considered on a case-by-case basis, one official said.

The European countries were expected to announce their side of the deal first today, followed later in the day by Secretary of State Condoleezza Rice’s announcement of the U.S. decisions, the officials said.

U.S. allies Britain, France and Germany are leading the diplomatic effort with Iran. Those countries wanted U.S. support on the theory that a united front was more likely to persuade Iran to comply. So long as the United States remained apart, Iran would delay meaningful steps to end its nuclear program, the Europeans argued.

They also argued that the United States risked looking like the odd man out if the Europeans did win a nonproliferation deal. The Europeans urged the United States to join the talks, but the Bush administration wanted to remain at arm’s length from Iran.

The U.S. support for a carrot-then-stick approach is a shift in Bush administration policy that up to now has opposed any reward for Iranian activities the administration views as a violation of the Nuclear Non-Proliferation Treaty. The treaty bars Iran from enriching spent nuclear fuel to make it suitable for nuclear weapons.

Up to now Bush, who also objects to Iran’s support of militant anti-Israeli groups like Hezbollah, has focused instead entirely on the possibility of U.N. sanctions against Iran.