In response, R. Nicholas Burns, an under secretary of state who is the chief American strategist on Iran, told the group that negotiations with Tehran could still be going on when Mr. Bush leaves office in January 2009. The hawks in the room reported later that they were deeply unhappy — but not surprised — by Mr. Burns’s assessment, which they interpreted as a tacit acknowledgment that the Bush administration had no “red line” beyond which Iran would not be permitted to step.

But conservatives inside the administration have continued in private to press for a tougher line, making arguments that their allies outside government are voicing publicly. “Regime change or the use of force are the only available options to prevent Iran from getting a nuclear weapons capability, if they want it,” said John R. Bolton, the former United States ambassador to the United Nations.

Only a few weeks ago, one of Mr. Cheney’s top aides, David Wurmser, told conservative research groups and consulting firms in Washington that Mr. Cheney believed that Ms. Rice’s diplomatic strategy was failing, and that by next spring Mr. Bush might have to decide whether to take military action.

The vice president’s office has declined to talk about Mr. Wurmser’s statements, and says Mr. Cheney is fully on board with the president’s strategy. In a June 1 article for Commentary magazine, the neoconservative editor Norman Podhoretz laid out what a headline described as “The Case for Bombing Iran.”

“In short, the plain and brutal truth is that if Iran is to be prevented from developing a nuclear arsenal, there is no alternative to the actual use of military force — any more than there was an alternative to force if Hitler was to be stopped in 1938,” Mr. Podhoretz wrote.

Mr. Burns and officials from the Treasury Department have been trying to use the mounting conservative calls for a military strike to press Europe and Russia to expand economic sanctions against Iran. Just last week, Israel’s transportation minister and former defense minister, Shaul Mofaz, visited Washington and told Ms. Rice that sanctions must be strong enough to get the Iranians to stop enriching uranium by the end of 2007.

While Mr. Mofaz did not threaten a military strike, Israeli officials said he told Ms. Rice that by the end of the year, Israel “would have to reassess where we are.”