WASHINGTON  In the aftermath of two major terrorist attacks on Western targets, America's counterterrorism community is warning that Al Qaeda may launch more overseas operations to influence the presidential elections in November.

Click Image to Enlarge AAMIR QURESHI/AFP/Getty A Pakistani army soldier stands guard by the devastated Marriott Hotel following an overnight suicide bombing at Islamabad on September 21, 2008.

Call it Osama bin Laden's "October surprise." In late August, during the weekend between the Democratic and Republican conventions, America's military and intelligence agencies intercepted a series of messages from Al Qaeda's leadership to intermediate members of the organization asking local cells to be prepared for imminent instructions.

An official familiar with the new intelligence said the message was picked up in multiple settings, from couriers to encrypted electronic communications to other means. "These are generic orders," the source said  a distinction from the more specific intelligence about the location, time, and method of an attack. "It was, 'Be on notice. We may call upon you soon.' It was sent out on many channels."

Also, Yemen's national English-language newspaper is reporting that a spokesman for Yemen's Islamic Jihad, the Qaeda affiliate that claimed credit for last week's American embassy bombing in Sa'naa, is now publicly threatening to attack foreigners and high government officials if American and British diplomats do not leave the country.

Mr. bin Laden has sought to influence democratic elections in the past. On March 11, 2004, Al Qaeda carried out a series of bombings on Madrid commuter trains. Three days later, the opposition and anti-Iraq war Socialist Workers Party was voted into power.

In the week before the 2004 American presidential election, Mr. bin Laden recorded a video message to the American people promising repercussions if President Bush were re-elected. In later messages, Al Qaeda's leader claimed credit for helping elect Mr. Bush in 2004. Last year in Pakistan, Qaeda assassins claimed the life of Benazir Bhutto, a former prime minister who returned to her native country in a bid for re-election.

"There is an expectation that Al Qaeda will try to influence the November elections by attempting attacks globally," a former Bush and Clinton White House counterterrorism official, Roger Cressey, said yesterday.

Mr. Cressey said Al Qaeda lacks the capability to pull off an attack in the continental United States, however. "It would likely be a higher Al Qaeda tempo of attacks against U.S. and allied targets abroad," he said.

At a talk at the Washington Institute for Near East Affairs on August 12, the national intelligence officer for transnational threats said he expected to see more threat reporting on Al Qaeda as America approaches the November elections.

The terrorist attack on the Marriott Hotel in Islamabad on Saturday was a particular blow to the allied effort against Al Qaeda. The hotel's lobby in recent years served as a meeting place for the CIA and Pakistanis who would not risk being seen at the American Embassy. The bombing, which targeted one of the most heavily fortified locations in Pakistan's capital, will likely claim close to 100 lives after the dead are pulled from the rubble.

President Zardari, who had just given his first major address as Pakistan's head of state, on fighting the Taliban and Al Qaeda, was the target of Saturday's attack, the vice president for research at the Foundation for Defense of Democracies, Daveed Gartenstein-Ross, said.

"He was expected to attend the iftar dinner at the Marriott," Mr. Gartenstein-Ross said "Think of the symbolic value if they were able to kill Zardari after his first address as president of Pakistan in a speech announcing his fight against the terrorists. The symbolic effect of the attack on the same day would be devastating."

An adviser to Senator McCain and a former director of central intelligence under President Clinton, James Woolsey, said Al Qaeda has a "history of doing three things at least related to elections. One is to attack before elections, such as in 2004 in Spain, and of course the assassination of Benazir Bhutto. They also have a history of attacks when new leaders take over, like Gordon Brown in Britain and the new leader in Pakistan, with the attack over the weekend. Also Al Qaeda sends messages to populations in elections. You really don't know which one of these they are going to implement."

Earlier this summer, another McCain campaign official mused in an interview that an attack could benefit his candidate in the polls. But whether that statement is true is unclear: At the Republican National Convention this month, Mr. McCain praised the president's counterterrorism policies for preventing an attack in America since September 11, 2001. The Bush administration has deliberately refrained from pointing to this success in light of the many plots that the president has said have been aborted on American soil since September 11.

The deputy communications director for the McCain campaign, Michael Goldfarb, said: "There is no doubt that Al Qaeda is still dangerous and still desires to strike at America and our allies. But Americans will not be intimidated and their votes will not be swayed by terror."

A spokeswoman for the Obama campaign, Wendy Morigi, said, "Last week's attacks demonstrate the grave and urgent threat that Al Qaeda and its affiliates pose to the United States and the security of all nations. As Senator Obama has said for some time, we must refocus our efforts on defeating Al Qaeda around the world."