LONDON - Prime Minister Tony Blair placed Britain on watch last night against terror attacks but coupled the alert with a word of caution that drastically curtailing activity in response to the threats would be conceding to terrorism.

"The dilemma is reconciling warning people with alarming them, taking preventive measures without destroying normal life," he said.

Using his annual speech to the Lord Mayor's Banquet in the City of London financial district, traditionally a forum for a foreign policy address, to focus on the terrorist threat to Britain, Blair acknowledged that the country was a target for al-Qaida.

But he added, "If on the basis of a general warning we were to shut down all the places that al-Qaida terrorists might be considering for attack, we would be doing their job for them."

Blair also took the occasion to underline the need for an expanded approach to security. "The world needs a broader agenda than simply terrorism and weapons of mass destruction," he said. "And we need full U.S. engagement and leadership on all of it. President Bush recognizes that."

Blair's comments followed a series of warnings in recent weeks from government officials and law-enforcement authorities in other European countries that al-Qaida might be broadening its targets beyond American and Jewish institutions and that Europe was at risk.

Last week, Ronald Noble, secretary-general of the France-based international policing authority Interpol, told the Paris daily Le Figaro that recent intelligence suggested that al-Qaida had been preparing to carry out simultaneous attacks in a number of countries.

"Something worrying is going on," Noble was quoted.

Officials in Germany have recently issued warnings since threats by an al-Qaida deputy, Ayman al-Zawahiri, against Germany and France were broadcast last month by the Arabic satellite television channel Al-Jazeera.

"The mujahid youth has already sent messages to Germany and France," Zawihiri said in the recording. "However, if these doses are not enough, we are prepared, with the help of Allah, to inject further doses."

In a television interview last week, August Hanning, director of the Federal Intelligence Service in Germany, warned that he believed that al-Qaida was planning a major attack, possibly in his country, though he did not say he had concrete evidence.

"We have to count on a new attack, an attack of a much larger dimension," he said. "There is a big threat, also in Germany."

French officials have taken a more cautious line. Responding on Saturday to news reports - including Noble's comments suggesting that France is a likely al-Qaida target - Prime Minister Jean-Pierre Raffarin said, "The interior-security council worked on all these questions, but the work is confidential."

In his speech, Blair pointed to the bombing in Bali on Oct. 12 that killed more than 190 people as unsettling evidence that attacks could occur anywhere at any time.

Another German official, Bodo Franz, director of criminal investigations at the Hamburg state police, also cited the Bali attack in a recent interview. "After Bali, it is becoming increasingly less clear what is being threatened," he said. "We can no longer limit potential targets. It keeps getting more diffuse"

But Blair asserted that the aftermath of the Bali blast also represented the danger of possible overreaction.

"If we acted on every piece of raw intelligence in a way that some were suggesting after Bali," he said, "we would have in my time as prime minister on many occasions shut down roads, railways, airports, stations, shopping centers, factories, military installations."