MESEBERG, Germany — President Bush yesterday raised the possibility of a military strike to thwart Tehran’s presumed nuclear weapons ambitions, speaking aggressively even as he admitted having been unwise to have done so previously about Iraq.

Mr. Bush’s host in two days of meetings at a baroque castle, Chancellor Merkel of Germany, made clear her views on the saber-rattling — however subtle — without directly countering her guest. “I very clearly pin my hopes on diplomatic efforts,” Ms. Merkel said, reflecting the deeply held European opinion that military action against Iran is nearly unthinkable.

Ms. Merkel joined Mr. Bush in urging further sanctions against Iran if it fails to suspend its uranium enrichment program.

Iran’s leader weighed in, too. Speaking before thousands in the central Iranian city of Shahr-e-Kord, President Ahmadinejad said Mr. Bush “won’t be able to harm even one centimeter of the sacred land of Iran” and promised continued defiance over Iran’s nuclear activities. Iran says it is enriching uranium to generate electricity, not build a bomb — a claim the West doubts is true.

“In the past two, three years, they employed all their might, resorted to propaganda … and sanctions,” Mr. Ahmadinejad said. “If the enemy thinks they can break the Iranian nation with pressure, they are wrong.”

Mr. Bush has alternated lately between slightly more conciliatory and slightly more forceful language on Iran.

Within the coded language of the American attitude toward Iran, several small changes in Mr. Bush’s rhetoric yesterday added up to a difference. Three times, he called a diplomatic solution “my first choice,” implying there are others. He said “we’ll give diplomacy a chance to work,” meaning it might not. He also offered, without even being asked a question about Iran, that “all options are on the table” — a longtime standard refrain, not heard as much lately, that neither confirms nor denies an intention to use military force.

There is no indication America actually plans any sort of military action, and experts believe it would be an extremely difficult feat tactically for many reasons. Mr. Bush’s back-and-forth talk appears designed more to both remind Iran that America is serious about keeping it from developing a nuclear bomb and to try to finally corral sometimes reluctant allies behind a common firm stand.

Mr. Bush’s chief aide on Europe, Judy Ansley, said Mr. Bush and Ms. Merkel did not discuss a military option in their meetings, only the diplomatic route.

But the German leader was strong on the need for new sanctions — through the United Nations but also possibly unilaterally by the European Union — if a package of incentives and penalties does not persuade Iran to halt its enrichment program. The European Union’s foreign policy chief, Javier Solana, is visiting Tehran soon to present the offer, an updated version of one developed five years ago by America, Germany, Britain, France, Russia, and China and ignored by Iran.

Ms. Merkel pointed to a recent report by the U.N.’s nuclear watchdog agency as proof that Iran is a problem. The group said that Iran has stonewalled its attempts to delve into allegations that several Iranian projects appear to represent different components of a nuclear weapons program. “We need to react to this … with further sanctions, if necessary,” she said.

Ms. Merkel also said European nations are newly committed to enforcing the three rounds of mild U.N. sanctions that already are on the books.

“We in the European Union will do everything to see to it that this actually happens,” she said.