WASHINGTON, Oct. 12 — American officials say they fear that attacks attributed to Al Qaeda in the past week and taped messages from the group's leaders signal the beginning of a new wave of terrorist activity and possibly a large-scale attack.

Senior government officials also say that a blast in Yemen that crippled a French oil tanker and that attacks in Kuwait that killed a United States marine demonstrated that the terror network had reconstituted itself, with smaller groups prompted to launch new attacks by inflammatory new messages from Qaeda leaders.

The group's latest round of attacks may be a response to the Bush administration's Iraq policy, the officials said. An audiotape of Osama bin Laden's closest lieutenant, Ayman al-Zawahiri, threatened continued attacks on "America and its allies," and denounced American plans to attack Iraq.

"The campaign against Iraq has an objective that is far beyond Iraq to reach the Arab and Islamic world," Mr. Zawahiri said on the tape. United States officials said his message appeared to be an attempt to justify and incite renewed violence against American targets.

Another audiotape, which officials say is of Mr. bin Laden, repeated Al Qaeda's threats against the United States. Both tapes were broadcast in the past week by Al Jazeera, the satellite channel based in Qatar, and one American official said the two messages might have been intended to be a green light for Al Qaeda to launch large-scale attacks.

Officials said that in the past week intelligence analysts had received reports of a spike in reported threats against the United States and American interests abroad.

"I'm afraid you'll see a lot more of this," said Senator Richard C. Shelby, an Alabama Republican. "We always warned that there would be more attacks because we have not finished off the Al Qaeda group. We've disrupted it. We've had them on the run, but they are still around."

The government's latest intelligence analysis is based in part on the tanker explosion off Yemen a week ago, and on the shooting of two American marines on an island off Kuwait on Tuesday, an attack that killed one and wounded the other.

Kuwait's interior minister said today that a statement from the gunmen's leader suggested a link to Al Qaeda and that the group had planned other attacks. [Page 17.] But other officials said it was not known whether the attackers were operating under direct orders from Al Qaeda's senior leaders.

"The marines in Kuwait and the ship off Yemen — those could be precursors of more to come," one senior administration official said. "We believe this is a serious development."

So far, the government's response to the two attacks has remained deliberately low key. On Wednesday, the Bush administration discussed whether to raise the color-coded threat alert warning level from yellow to orange. But after a White House meeting, officials decided the threat was not yet specific enough.

Instead, the Federal Bureau of Investigation and the Office of Homeland Security issued a threat alert to the country's 14,000 state and local police agencies, saying the recent messages showed that "Al Qaeda continues to plan major attacks against U.S. interests."

"The statements suggest that an attack may have been approved," the alert said, "while the specific timing is left to operatives in the field."

The threat warning said Al Qaeda had issued similar messages before the bombing of two American embassies in East Africa in August 1998. "The content of the statements and the context surrounding these threats reinforces our view that they may signal an attack," the message said. "One senior detainee maintains that Al Qaeda would only release such a statement after approving a specific plan for an attack."

Officials are also concerned that another large-scale attack, perhaps in the United States, could be imminent because it usually takes at least one year for Al Qaeda to organize an ambitious attack. Nearly a year separated the attack on the American destroyer Cole in a port in Yemen in October 2000 and the Sept. 11, 2001, attacks against the World Trade Center and the Pentagon.

The latest wave may be linked to earlier attacks this year. In June, a suicide bomber blew up a truck outside the American Consulate in Karachi, Pakistan, killing 14 Pakistanis. Since then, the authorities have linked Al Qaeda to at least five attacks or thwarted attacks, though none in the United States.

Even if terror groups do not launch another large and concerted strike, officials say, the concern is about small groups of Qaeda members carrying out attacks in the United States that are similar to the recent ones in Kuwait and Yemen.

"There are remnants that are still out there somewhere, and they still have all that training," one senior government official said. "They may come in groups of ones and twos and threes. Small arms, chemicals or explosives, it's all right here."

For months, senior officials feared Al Qaeda would emerge after its members' escape from Afghanistan as a more dispersed but deadly network that would be far more difficult to contain. They worried that the network's old hierarchy, led by Mr. bin Laden, had been replaced by tactical operatives with makeshift alliances to militant groups in countries like Pakistan, Egypt, Algeria and Yemen.

The issue of whether Mr. Zawahiri survived the war in Afghanistan seemed to be settled by the release of the recording with references to recent events, like the Iraq debate. But the absence of video images of Mr. Zawahiri suggested to some analysts that he had been injured or had somehow changed his appearance to elude capture.

In the taped message, Mr. Zawahiri also takes credit for several recent terrorist attacks, including several against German and French targets in the Middle East. One goal of American policy, he said, was to make Israel the dominant power in the region. Another objective, he said, was to divide Saudi Arabia into four regions, with its oil fields under the direct control of the United States.

Intelligence officials said they thought that the voices on the audiotapes were those of Mr. bin Laden and Mr. Zawahiri. But they said that only the Zawahiri tape appeared to be recent, possibly recorded within the past month and no later than last summer, officials said.

Greater skepticism surrounds the bin Laden tape, released on Oct. 6 by Al Jazeera. In it, he refers to the Sept. 11 attacks as having already occurred but does not cite any other specific events that could be used to date the recording.

Mr. Zawahiri said in his tape that Mr. bin Laden and Mullah Muhammad Omar, the Taliban leader, had survived the war. But the tape provided no evidence to support that claim, and officials remain divided over whether Mr. bin Laden is alive. But they say that Mullah Omar survived the war and is in hiding.

The tape thought to be of Mr. bin Laden contained an anti-American message that is familiar from his previous video and audio messages. "Let America increase the pace of this course of conflict or decrease it," it says, "we will retaliate in kind, God willing, and, God is our witness, that the men of Islam are preparing for you what would fill your hearts with terror, and they will target the hinges of your economy until you stop your injustice and aggression or either one of us dies first."