An audiotape attributed to al Qaeda's second-in-command, Ayman Zawahiri, emerged yesterday, calling for preemptive attacks against the United States and its allies, and urging followers to continue fighting "if we die or are arrested."

The tape, broadcast on the al- Jazeera satellite network, is the second message in less than a month to be attributed to Zawahiri, who is believed to be directing limited al Qaeda operations from hideouts along the Pakistan-Afghanistan border.

The recording stoked fears among some U.S. and European intelligence officials that the terrorist network is preparing a significant strike before the Nov. 2 presidential election. The FBI and other agencies this week launched an aggressive campaign of interviews and arrests aimed at thwarting such an attack.

The tape contains no specific clues indicating when it might have been recorded, and is notably downbeat compared with previous triumphal messages from al Qaeda. It bemoaned a lack of action against "the Americans and the crusaders" and called on "Muslim youth" to form a new leadership to fight Western powers.

"Let us start resisting now," the speaker says on the tape, according to a Reuters translation. "We can't wait any longer, or we will be eaten up country by country, just as they occupied us in the last two centuries. . . . The Muslim world has entered a new age of occupation and dividing into sphere of influence."

In one passage, Zawahiri also mentions the possibility of dying or being captured, presumably referring to himself and other fugitive al Qaeda figures. The network's leader, Osama bin Laden, has not been heard from since the release of an audiotape in May.

State-run Pakistani television reported yesterday that security forces had killed about 100 suspected al Qaeda terrorists during a recent military operation in tribal areas near Afghanistan, according to the Associated Press. The broadcasts quoted Pakistan's president, Gen. Pervez Musharraf.

Intelligence analysts have "high confidence" that the voice on yesterday's audiotape belongs to Zawahiri, based on a preliminary technical analysis, one U.S. official said.

Since the Sept. 11, 2001, attacks, the emergence of such tapes from bin Laden and other al Qaeda figures has prompted concern among intelligence officials and terrorism experts, who say they often presage terrorist attacks by a month or two.

A government official with access to daily terrorism intelligence reports said: "There is a concern among people that today's warning seems similar to the warning that preceded the 1998 U.S. embassy bombings in Africa and other calls to arms that came to forecast attacks. It seems to be a green light to attack," as opposed to attacking in a more limited way.

"Given past patterns, this tape validates all the concerns we've had about the period leading up to the elections," said Bruce Hoffman, a terrorism expert who heads Rand Corp.'s Washington office. "This ratchets up one's sense of alert to expect something somewhere."

Several terrorism experts also said there is a note of desperation to the message, as well as an apparent acknowledgment that U.S. and Russian military actions in Iraq, Afghanistan, Chechnya and elsewhere are affecting the organization. Zawahiri explicitly calls for the creation of "a leadership for the resistance to combat the crusaders."

European security officials said yesterday that they were still assessing the tape to determine whether the speaker is Zawahiri. He cited Britain, France, Norway and Poland as European nations that deserve to be targeted for attacks because of their support for Israel or the U.S.-led invasion of Iraq.

In an interview before the tape was made public, a senior German intelligence official said he was "convinced" that Zawahiri and bin Laden are in hiding along the border between Afghanistan and Pakistan, where U.S. and Pakistani forces have concentrated an unsuccessful search for nearly three years. Although the Bush administration has said it has captured or killed much of al Qaeda's leadership since the attacks, the German official said the network can still plan attacks or give orders from its base in Pakistan and Afghanistan.

"Of course, they've suffered heavy losses," the official said, "but we have seen that they have always managed to replace these top people with younger people. These people may not be as experienced, but they are still effective."

Zawahiri's broadcast comes as the FBI and other U.S. agencies embark on an aggressive campaign aimed at thwarting any plans for an attack before or during the November elections. The FBI has also interviewed more than 13,000 immigrants this year as part of a broader effort to gather information about suspected terrorist groups, law enforcement officials said.

Department of Homeland Security officials said yesterday they are stepping up efforts to arrest visa violators who may pose a threat to the country.

Dean Boyd, a spokesman for the department's Immigration and Customs Enforcement bureau, said a special ICE unit had arrested 359 foreign nationals on visa violations between June 2003 and August 2004. Those arrests resulted from nearly 5,200 field investigations carried out by the Compliance Enforcement Unit, which tracks foreign students and other visitors who violate their immigration status.

Boyd said that "some" of those arrested were linked to cases involving national security, but he did not have a number.

Correspondent Craig Whitlock in Berlin and staff writer Mary Beth Sheridan and researcher Julie Tate in Washington contributed to this report.

"Let us start resisting now," Ayman Zawahiri says on new tape.