Washington ? The United States said Wednesday it would join in face-to-face talks with Iran over its disputed nuclear program if Tehran first agreed to put challenged atomic activities on hold, a shift in tactics meant to offer the Iranians a last chance to avoid punishing sanctions.

Iran dismissed the offer as “a propaganda move.”

Before leaving for meetings in Europe on Iran, Secretary of State Condoleezza Rice said that while the U.S. was willing to join talks between European nations and Iran, it was also helping to prepare a package of sanctions that Tehran could face should it decline the new offer.

“We’re prepared to go either way,” she said.

At the White House, President Bush said, “I believe that it’s important that we solve this issue diplomatically, and my decision today says that the United States is going to take a leadership position in solving this issue.”

The overture to join stalled European talks came after mounting pressure on the U.S. from European allies.

The administration is convinced Russia and China would support sanctions or other harsh measures if new talks fail to persuade Iran to abandon nuclear efforts that the West fears could lead to a bomb, said a senior administration official. The official briefed reporters on condition of anonymity because the secretary was continuing talks with other countries.

Rice will be working to reaffirm such support on Thursday.

The Iranian news agency said Iran accepts only proposals and conditions that are in the nation’s interest. “Halting enrichment definitely doesn’t meet such interests,” IRNA said.

The United States has had no diplomatic ties with Iran and few contacts at all with its government since Islamic radicals took over the U.S. Embassy in 1979 and held diplomats for more than a year.

Rice will meet with foreign ministers from the other permanent U.N. Security Council members on Thursday in Vienna to finalize a package of economic incentives and threats to be presented to Tehran. That package would be on the table in any new talks involving the United States.

The Bush administration had until now refused to talk directly to the Iranians about their nuclear program, although there have been sporadic contacts among relatively low-level officials on other subjects. The U.S. has long rejected direct contacts because it says Tehran supports terrorism and because it wants to avoid appearing to legitimize the regime.

The offer to talk should strip Iran and some U.S. allies of the argument that the hardline U.S. stance was an obstacle, or that Washington was not willing to try every means to resolve the impasse peacefully, U.S. officials said.

“This is the last excuse, in some sense,” Rice said.

She said the United States was not offering full diplomatic relations with Iran and would not swear off ever using military action to stop what the U.S. contends is a rogue program to build a nuclear weapon.

“This is not a grand bargain,” Rice said. “What we’re talking about here is an effort to enhance the chances for a successful negotiated solution to the Iranian nuclear problem.”