The nation's top law enforcement officials, saying they are convinced al Qaeda is planning an attack on the United States in the coming months, issued an urgent plea yesterday for information about seven people who they said could be involved in such an effort.

FBI Director Robert S. Mueller III asked for the public's help in tracking down six men and one woman associated with al Qaeda who either are familiar with the United States or have a history of involvement in attacks on U.S. interests.

All but one -- Adam Yahiye Gadahn, 25, a Southern California convert to Islam linked to top al Qaeda captive Abu Zubaida -- have been sought for many months by the FBI. Officials said they do not know whether any of the seven is in the United States.

"We need the public -- both in the United States and overseas -- to be on the lookout for these seven individuals," Mueller said at a packed news conference. "Have you seen them in your communities? Have you heard that someone might be helping them to hide?" If so, he said, "we need you to come forward."

Just hours before Mueller and Attorney General John D. Ashcroft spoke, however, Homeland Security Secretary Tom Ridge appeared on five television networks telling the public to proceed with holiday plans and normal routines.

Ridge acknowledged the government's concern about the danger of an attack, but he offered a reassuring message as a counterbalance to the serious warnings from Ashcroft and Mueller.

"We need Americans to just go about living their lives and enjoying living in this country," Ridge said on CBS's "Early Show."

"America's job is to enjoy living in this great country and go out and have some fun," he said on CNN.

Ridge said there are no immediate plans to raise the color-coded terrorism threat level because the threat information is not specific enough.

The result was a message that left some saying that the government has offered little new information. "I haven't gotten specific information at all," said D.C. Police Chief Charles H. Ramsey. "We have been talking about different events taking place this summer for a while," he said, adding: "The city itself is a target -- we already know that."

The government is tightening security for ceremonies inaugurating Washington's National World War II Memorial on Saturday and for other Memorial Day events, as well as security for the Group of Eight meeting of industrialized nations in Georgia next month; the two political parties' nominating conventions, in Boston and New York; the Summer Olympics in Greece; and the presidential inauguration next January.

Ashcroft and Mueller said they do not know where or how attacks might be attempted, but they noted that there are indications terrorists want to mount an attack that would affect the upcoming national elections, as they had done in Spain with the March 11 Madrid train bombings

"Credible intelligence, from multiple sources, indicates that al Qaeda plans to attempt an attack on the United States in the next few months," Ashcroft said. "This disturbing intelligence indicates al Qaeda's specific intention is to hit the U.S. hard." He said the information has been "corroborated on a variety of levels."

But he and Mueller also acknowledged that they are not certain any of the seven suspected al Qaeda associates is participating in the attack planning. They said FBI agents across the country will launch a new round of interviews in Muslim communities to try to develop information.

FBI officials are particularly worried about Adnan G. El Shukrijumah, a Saudi native who lived in South Florida in the mid-1990s. "We know that he has been involved in terrorist planning with senior al Qaeda leaders overseas and has scouted sites across America that might be vulnerable to a terrorist attack," Ashcroft said. Shukrijumah has made repeated attempts to get back into the United States using false passports, he said.

The attorney general said al Qaeda's public statements indicate its intentions. Just after New Year's Day, al Qaeda announced that plans for an attack on the United States were 70 percent complete, he said. After the March bombings that killed 191 in Madrid, he added, an al Qaeda spokesman said plans were 90 percent complete.

Others the FBI is seeking are Aafia Siddiqui, a Pakistani woman who has a doctorate and studied at the Massachusetts Institute of Technology; Ahmed Khalfan Ghailani, a Tanzanian under indictment in New York for his alleged involvement in the 1998 embassy bombings in East Africa; Fazul Abdullah Mohammed of the Comoros Islands, also indicted in the embassy bombings; Amer El-Maati, a Canadian citizen born in Kuwait; and Abderraouf Jdey, a Canadian citizen born in Tunisia who appeared in a "martyrdom" video recovered in Afghanistan.

The warning quickly became a partisan issue yesterday.

"I know that every American who watched the news last night or picked up the paper this morning was struck by the seriousness and the concern coming from this administration," said Democratic presidential candidate John F. Kerry. He said the threat points up the Bush administration's failure to make trains and chemical plants safer from attack and to inspect containers coming into the nation's ports. The senator from Massachusetts added: "We deserve a president of the United States who doesn't make homeland security a photo opportunity and the rhetoric of a campaign."

But administration officials said they are going to extraordinary lengths to secure the upcoming events.

Government officials said the biggest problem with the G-8 meeting is that its events will be spread out over dozens of sites across a 50-mile swath from Savannah, Ga., to Jacksonville, Fla. Many will be held in relatively secluded resort locations, including the G-8 summit meeting on Sea Island, Ga.

"We will be at the greatest level of security of any national event in our history," Asa Hutchinson, undersecretary of homeland security, said in an interview.

For July's Democratic convention in Boston, the Secret Service and local authorities have decided to shut down the highway next to Fleet Center each evening and to bar traffic in the area around the convention center. Subway operations will also be interrupted. But in Manhattan, officials will allow subways and trains to run under and alongside the GOP's Madison Square Garden convention site.

U.S. officials said they also fear that, far from these high-visibility, symbolic locations, terrorists could mount multiple attacks using car or truck bombs, or explosives detonated by remote control, on "soft targets." These include shopping malls, trains, train stations, hotels, tourist sites, churches and synagogues.

Several airport and aviation officials said yesterday that they had not been informed of any new warnings by Department of Homeland Security officials concerning the terrorist threats, nor had they been directed to step up security.

Terrorism experts said that besides measures to control traffic flow and to erect security barriers in some locations, the government has very limited ability to guard against terrorist attacks on soft targets. Among the available tactics, they said, is what Ridge did yesterday in several television interviews: enlisting members of the public to be on the alert for signs that something is amiss.

Staff writers Sara Kehaulani Goo and Spencer S. Hsu contributed to this report.

Amer El-Maati Aafia Siddiqui Adnan G. El Shukrijumah Fazul Abdullah Mohammed Adam Yahiye Gadahn Abderraouf Jdey Ahmed Khalfan Ghailani "We need the public -- both in the United States and overseas -- to be on the lookout for these seven individuals," FBI Director Robert S. Mueller III said.