BERLIN — With mystery enveloping a German intelligence service employee accused of spying — reportedly for the United States — German officials and commentators on Sunday angrily demanded a response from Washington, warning that an already troubled relationship was at risk of deteriorating to a new low.
The demands for a statement from the United States were nevertheless couched in cautious terms, suggesting that the scandal, which exploded on Friday when Germany’s federal prosecutor reported the arrest of the 31-year-old employee of the Federal Intelligence Service, might not be as bad as initially feared. The chairman of a parliamentary inquiry into American intelligence activities told German radio that it seemed there was no breach of security surrounding his committee’s work, as some news reports had suggested.
Still, the anger was palpable. President Joachim Gauck, whose role is largely ceremonial but who increasingly speaks out on daily matters, told German television that if it turned out that the United States had been spying on Germany, “then that is really a gamble with friendship, with a close alliance.”
“Then we really have to say, ‘Enough,’ ” Mr. Gauck added.
Chancellor Angela Merkel, on a trip to China, kept silent on the matter, although reporters traveling with her cited unidentified people in her circle as saying she was “surprised” and “disappointed” at the suggestion that an American intelligence agency had recruited a German agent. Foreign Minister Frank-Walter Steinmeier, traveling in Mongolia, was quoted in the German news media as saying that “if the reports are true, then we are not talking about something minor.”
The United States “should fully explain the matter as soon as possible,” Mr. Steinmeier added.
Perhaps the most striking sign of the strained relationship was Germany’s decision to summon the American ambassador, John B. Emerson, to the Foreign Ministry on the Fourth of July, just before the American Embassy’s holiday party for hundreds of guests. The newsmagazine Der Spiegel reported that the ambassador had smiled and greeted guests, but that the tension was noticeable: “It was as it has so often been recently when official America meets official Germany. The facade was perfect, but behind it there was little accord.”
An American whom Germans did hear from during the weekend was Hillary Rodham Clinton, in Berlin to promote the German-language edition of her recent book, “Hard Choices,” about her years as secretary of state. While skirting judgment on the new espionage scandal, she emphasized at a Saturday reception at the ambassador’s residence that the relationship between the United States and Germany was valued, and should not be “sidelined, downgraded or destroyed.”
At an appearance on Sunday, she said, “Let’s find out what the facts are,” noting that relations “should not be put at risk.”
Over decades of friendship since 1945, sharp language like that of recent months has been rare in German-American dealings. Those ties have been strained since last summer, when documents leaked by Edward J. Snowden, a former National Security Agency contractor, suggested that the N.S.A. had monitored the electronic data of millions of Germans.
The German government then appeared to receive assurances from Washington that nothing illegal had occurred. But the subsequent revelation that Ms. Merkel’s own cellphone had been monitored stirred new anger in a nation that remembers the role played by a snooping state under the Nazis and the Communists.
The German government tried reaching a “no spy” accord with Washington, but the Obama administration rejected the idea. Months of attempts to restore relations have yielded the beginnings of a dialogue about how to deal with electronic data, cybersecurity and privacy.
Those talks, and much else, would be jeopardized if the Americans recruited an agent, German commentators warned.
Stefan Kornelius, the foreign editor of the newspaper Süddeutsche Zeitung and usually a pronounced Atlanticist, wrote a blistering commentary on Saturday, saying it was hard even to summon words to describe the potential damage.
If United States intelligence agencies acted as suggested, he wrote, that would be “either stupid or shameless.” Either way, relations would turn icy, because confirmation of the espionage accusations would mean either that President Obama does not have the intelligence services under control, or that he lied when trying to smooth things over in recent months, Mr. Kornelius said.
“The United States must now make plain publicly in whose name, and why, the German partner service was infiltrated,” Mr. Kornelius added. “Whoever is responsible for this damage must go — in Washington just as in Berlin.”
The response to Mrs. Clinton by contrast testified to the warm feelings many Germans have for Americans.
Welcomed by 1,000 people who paid up to $27 each to pack a theater on a sweltering Sunday morning, Mrs. Clinton regaled her audience with anecdotes from meetings with President Vladimir V. Putin of Russia, Ms. Merkel and other world leaders.
Sandra Koch, 26, who works for an economic association in Berlin, was one of several young professional women who said they felt inspired by Mrs. Clinton’s career as lawyer, activist, first lady, wife, mother, senator and secretary of state.
“For any young woman who wants to achieve something, she is a role model,” Ms. Koch said as she joined scores of others in a line to buy Mrs. Clinton’s book, in German or English.
Holger Sieversen, 66, a lawyer, said he had attended the event “because there is a chance that Mrs. Clinton could be president of the United States, and I wanted to see her, and most importantly listen to her in person.”
“I am a West Berliner,” he added, alluding to what the city endured until the Berlin Wall fell in 1989. He had no illusions: Countries spy on one another, but “at least should not get caught.”
“That is embarrassing,” he said, “and it costs.”