Attorney General John Ashcroft and FBI Director Robert Mueller scheduled a news conference to outline an intensive effort by law enforcement, intelligence and homeland security officials to detect and disrupt any potential plots.
CBSNews.com will Webcast the Ashcroft/Mueller news conference, scheduled to begin at approx. 2 p.m. EDT.
CBS News Chief White House Correspondent John Robertsreports that Ashcroft and Mueller planned to distribute the names and photographs of several individuals they wish to
U.S. counterterrorism and law enforcement officials say intelligence indicates that a group of terrorists already deployed inside the United States is preparing to launch a major attack this summer.
The intelligence was described Tuesday by a senior counterterrorism official on condition of anonymity as extremely credible and backed by an unusually high level of corroboration.
"There is clearly a steady drumbeat of information that they are going to attack and hit us hard," the official said.
White House press secretary Scott McClellan says there is "credible information that suggests there may be people in place who want to carry out attacks on the U.S."
"We are ramping up efforts to disrupt attacks," McClellan said.
The FBI was dispatching a bulletin to some 18,000 state and local law enforcement agencies warning of the threat.
The intelligence is among the most disturbing received by the government since the al Qaeda attacks of Sept. 11, 2001, the official said.
However, it does not include a time, place or method of attack.
And despite the worries, there was no immediate plan to raise the nation's terrorism threat level from yellow, or elevated, to orange, or high. The threat level has been at yellow — midpoint on the five-color scale — since January.
"Every single day it's our job within the Department of Homeland Security to work with federal, state, local officials in the companies in the private sector to get smarter and more secure, Ridge said. "We don't need to raise the threat level to bring together some of the best and brightest minds in this country to use people and technology to be
Ridge said people should "go about living their lives as Americans. We'll provide the security, they have to figure out how to have fun themselves."
A federal security official told CBS News Correspondent Bob Orr, "We know of no new specific highly credible intelligence suggesting an imminent attack … there's nothing we would characterize as an increase in the chatter level."
What has increased concern is the long list of high-profile events taking place this summer. Each could pose a tempting target for terrorists.
The events include Saturday's dedication of the new World War II Memorial in Washington, the G-8 summit in Georgia next month that will attract top officials from some of America's closest allies, the Democratic National Convention in Boston in July and the Republican National Convention in August in New York City.
The FBI and Homeland Security Department also are concerned about so-called soft targets such as shopping malls anywhere in the United States that offer a far less protected environment than a political convention hall.
Of special concern, the counterterrorism official said, is the possibility that terrorists may possess and use a chemical, biological or radiological weapon that could cause much more damage and casualties than a conventional bomb.
While the government has worried for years that al Qaeda may try to get its hands on such weapons, CBS News has learned that it is a recent bomb plot in Saudi Arabia that has them truly worried. The plot illuminated a new tactic to attack large fortified public-like buildings.
Terrorists planned to use two truck bombs — one to blow up outside defenses, and a second to drive through the opening — and take down the building.
The FBI already has created a special task force that is focused solely on dealing with this summer's threat. The task force, whose existence until recently was classified, is intended to ensure that no valuable bits of information or intelligence fall through the cracks, as happened before the Sept. 11 attacks.
Other actions to be taken include new FBI interviews with people who may have provided valuable information in the past, distribution of photos of individuals sought for questioning and a fresh examination of older investigative leads to determine whether they might point to elements of the summer plot.
U.S. authorities have said repeatedly that al Qaeda is determined to mount an attack on U.S. soil, in part to announce to the world that it remains capable of doing so despite the money and effort that has gone into homeland security since the Sept. 11 attacks.
The official did not say how many suspected al Qaeda or other terrorist operatives are believed in the country, whether they made their way into the United States recently or have been here for some time. The FBI has warned in the past that Islamic extremist groups may attempt to recruit non-Middle Easterners or women for attacks because they would be less likely to arouse suspicion.
Special security attention already is being focused to the nation's rail, subway and bus lines. The FBI last week sent out an intelligence bulletin to law enforcement agencies urging vigilance against suicide bombers, who have been used by terror groups worldwide to devastating effect but not so far in the United States.