OMAHA, Neb. — President Bush, trying to keep pressure on Iran, called on Tehran today to “come clean” about the scope of its nuclear activities or else face diplomatic isolation.

Two days after a new intelligence report said that Iran had halted its nuclear weapons program four years ago, Mr. Bush demanded that Tehran detail its previous program to develop nuclear weapons “which the Iranian regime has yet to acknowledge.”

“The Iranians have a strategic choice to make,” he said. “They can come clean with the international community about the scope of their nuclear activities, and fully accept the long-standing offer to suspend their enrichment program and come to the table and negotiate, or they can continue on a path of isolation.”

The administration is worried that the new National Intelligence Estimate — representing a consensus of all American spy agencies — weakens its leverage over Iran and its ability to build global pressure on Tehran to stop its uranium enrichment program.

Mr. Bush, arriving here on a campaign fundraising trip, said he had consulted with members of his national security team, who gave him a report about what Secretary of State Rice and the national security adviser, Stephen Hadley, have learned in talks during the past several days with their counterparts in Britain, Germany, France, and Russia.

“These countries understand that the Iranian nuclear issue is a problem, and continues to be a problem and must be addressed,” Mr. Bush said.

Backing the American intelligence community, Mr. Bush said he appreciated its work in helping people to understand past and present activities in Iran and helping the administration develop a sound policy.

“It is clear from the latest NIE that the Iranian government has more to explain about its nuclear intentions and past actions,” Mr. Bush said.

His statement today came a day after a news conference called in part to react to the new information on Iran’s nuclear activities. Mr. Bush’s public remarks, coupled with frenzied contacts with world leaders by Mr. Bush, Ms. Rice and Mr. Hadley, show a White House trying to keep the world on board with its hard line against Tehran — an uphill effort now, according to most analysts.

Also today, the White House said America will continue “actively pushing” for a third, tougher round of United Nations sanctions against Iran. A White House spokesman, Tony Fratto, said Iran continues to hide information, remains in violation of two U.N. Security Council resolutions, tests ballistic missiles, and is enriching uranium.

“Anyone who thinks that the threat from Iran has receded or diminished is naive and is not paying attention to the facts,” Mr. Fratto told reporters flying aboard Air Force One with Mr. Bush en route to Nebraska.

Mr. Fratto disputed Iran’s claim that the intelligence estimate was a vindication for Tehran. “I think that’s absolutely absurd, and Iran should take no comfort or vindication from the NIE,” he said.

He rejected calls, since the new report, for the administration to enter into unconditional talks with Iran, something the White House has said it would only do once Tehran stops enriching uranium.

Tehran says its nuclear program is only for civilian energy purposes. It says it is allowed to enrich uranium for that reason.

Mr. Rice, traveling in Africa today, questioned the openness of the Iranian government after President Ahmadinejad said the new American intelligence review amounted to “a final shot” against Tehran’s critics.

Mr. Rice declined to respond to Mr. Ahmadinejad’s remark, but told reporters in the Ethiopian capital of Addis Ababa that the public release of the NIE showed the administration was committed to transparent democracy, while Iran was not.

“I am not going to comment on that comment except to say that what the National Intelligence Estimate shows, and the transparency with which the administration released it, is what it means to live in a democracy and I hope one day that the people of Iran will live in a democracy too,” she said.

Mr. Rice said that the latest American intelligence estimate did not mean that Washington no longer considered Tehran a threat and urged the international community not to back down at the U.N. Security Council on pressuring Iran to halt its activities that could produce the ingredients for an atomic weapon.

“It is the very strong view of the administration that the Iranian regime remains a problematic and dangerous regime and that the international community must continue to unite around the Security Council resolutions that have passed,” she said.

“Iran needs to stop enrichment and reprocessing activities because those enriching and reprocessing activities permit, if they are perfected, a state to acquire fissile material for a nuclear weapon,” Ms. Rice said.