These officials refused to describe that information, except to say it was not the kind that would stand up in court. But it was used, administration officials say, to try and exploit a deepening power struggle within Iran's government and see if Mr. Khatami was ready, or able, to split from the hard-liners and disavow his country's long support of terrorism.

A message from Mr. Clinton to Mr. Khatami was secretly drafted, requesting his cooperation in the Khobar case and asking him to try and stop other terrorist-related activities. That message sat unsent in the White House for months, until August, when it was finally delivered by Assistant Secretary of State Martin Indyk and a National Security Council aide, Bruce Reidel, at a meeting in Paris with officials from Oman, who passed it on.

While the message had been addressed personally to Mr. Khatami, the response came back from the government of Iran: it was not interested. Though the attempt failed, it was just one signal that Washington was eager to settle old disputes and deal with Tehran.

The administration has also gradually moved to soften economic and trade sanctions against Iran, which have in any case proven porous as American allies in Europe trade with Iran and have begun to normalize their relations with Tehran.

In April, the White House announced an exemption of commercial sales of food, medicine and medical equipment, enabling bulk sales of American grain to Iranian buyers. Last month, the Royal Dutch/Shell Group announced that it had reached an agreement with Iran to spend $800 million to develop two Iranian offshore oil fields.

American law prohibits investments of more than $40 million a year in Iran. Shell, with headquarters in Amsterdam and London, has large operating units in the United States, but a company official said it expected Washington to waive the sanctions, as it has with other oil companies that have signed contracts with Iran.

As the economic barriers start to slip, the administration continues to pursue what it calls its people-to-people initiatives, including visits of Iranian wrestling teams, scholars and artists to the United States.