Agencies across the federal government are launching an aggressive and unusually open offensive aimed at thwarting terrorist plots before and during the presidential election in November.

Numerous law enforcement and counterterrorism officials also warned last week that a heightened threat of terrorist attack will persist through the January inauguration.

The government's strategy will include heavy surveillance by the FBI, increased checks of terrorism watch lists by local police and heightened security at polling places on Nov. 2, officials said. At the U.S. Capitol, Police Chief Terrance W. Gainer has ordered a number of his officers to wear sophisticated new equipment to protect them from a biological or chemical attack.

Counterterrorism officials concede they do not have new or specific intelligence outlining plans for an attack, but they say they remain alarmed by indications that al Qaeda and other terror groups might seek to influence U.S. elections as they did in Spain last spring by setting off bombs on commuter trains in Madrid. By publicizing the government's disruption efforts, which will begin in earnest later this week, authorities say they hope to forestall any plans for similar attacks here.

The FBI, which is sharply limiting personal leave and transferring hundreds of agents to the effort, will focus heavily on individuals within the United States who are suspected of having ties to al Qaeda and other terrorist groups or who sympathize with their causes, according to officials who have been briefed on the plans.

Officials said the FBI's tactics, which will be outlined in an electronic communication to be sent to field offices this week, will include aggressive and often overt surveillance, widespread interviews and, in some cases, arrests. Local police will be urged to run the names of suspicious people through the federal government's terrorism watch list, even during traffic stops and other minor encounters.

"We are always asking ourselves the critical question, 'Have we done everything we can to thwart the next attack?' " said Michael A. Mason, who heads the FBI's Washington field office. "We ask ourselves that every day."

The warnings are reminiscent of those this summer when officials expressed extreme concern about the potential for terror attacks on the Republican and Democratic national conventions and at the Olympic Games in Athens. Those events passed without any known disruption.

Earlier this month, the FBI's " '04 Threat Task Force" issued an advisory saying there was no intelligence detailing the timing, status or targets of any plot, but it said an increased threat of terrorist action will continue through the Jan. 20 inauguration, according to sources with access to the memo. The bulletin indicated that New York, Los Angeles, Chicago and Washington -- the nation's capital and three largest cities -- were cities of interest, but also mentioned others, these sources said.

A national election security planning bulletin will be sent today to the 50 states and the District, containing guidelines to governors and election officials for coordination of law enforcement, polling place and ballot-counting security, legal powers to order emergency election changes and public communication from now through Election Day.

Authorities are focused on a series of dates, starting with the annual meetings that begin Friday at the International Monetary Fund and the World Bank, both of which remain under a heightened "orange alert" along with other potential financial targets in Washington, New York and New Jersey. State and federal officials said the threat window will remain open through the Nov. 2 elections, the Dec. 13 electoral college ballot and the inauguration.

Agents from various federal departments have begun visiting rental car and truck firms across the country, as well as limousine companies, to urge them to be on heightened alert for suspicious activity that might indicate a planned car- or truck-bomb attack. Airline security officials have tightened procedures at airport checkpoints to hunt for explosives that might be hidden under a passenger's clothing.

Friday on Capitol Hill, officers scattered throughout the area were wearing new "Level B Training" vests and carrying protective hoods. Mario Tonzelli, who has been on the force for two years and was working at First Street and Constitution Avenue NW, said the new vest weighs about 40 pounds "but at the end of the day feels like 200 pounds."

The black nylon mesh vest contains several pockets. A one-time-use escape hood with special filters is attached to the side and a chemical-biological hazard suit is sealed up in the back of the vest along with gloves and rubber boots. Tonzelli and the other officers underwent 40 hours of special training before they were issued the equipment.

Even as security is tightened, however, numerous counterterrorism and law enforcement officials concede that the activity is not based on any new or specific intelligence. Some officials also say they are concerned that people may become inured to the drumbeat of warnings about the terrorist threat, especially given the lack of incidents during the political conventions and Olympics.

James M. Loy, the deputy secretary of Homeland Security, said in an interview Friday that even if there is no attack between now and the inauguration, officials will be just as worried about other events well into 2005 and beyond.

"I call it the new normalcy," Loy said. "We're immersed [in a war] with the first 'ism' in the 21st century. . . . We must find a way to hold onto the sense of urgency, and hold it potentially for decades."

Homeland Security has taken dozens of steps that now will be more or less permanent, Loy said, including stepping up inspections of train tracks, increasing Coast Guard boardings of incoming cargo ships and expanding the use of explosive-sniffing canine units.

U.S. intelligence officials said they continue to sift through al Qaeda computer documents retrieved during a series of raids in Pakistan over the summer.

The computer files, which included photographs and other information gleaned from the surveillance of U.S. targets before the Sept. 11, 2001, attacks, prompted Homeland Security Secretary Tom Ridge to raise the terror threat level for the financial sectors.

But several sources who have been briefed on the results, and who declined to be identified because the material is classified, said little fresh information has been gleaned.

The files included information about radiological devices, but there was no data linking that information with plans to attack the United States. Nor were there indications that members of al Qaeda had acquired the components for such a device, according to an official who has read recent intelligence reports.

One senior European intelligence official said his country has seen no direct evidence that al Qaeda has the ability or specific intent to launch an attack in the United States before the November elections. Regardless, the official added, al Qaeda is benefiting from widespread fears that they are plotting something.

Although U.S. law enforcement officials are short on specifics, they said their agencies have been stepping up their counterterrorism efforts. Vacations have been canceled. Off-site locations have been set up in case agency personnel have to be moved out of Washington. At the Bureau of Alcohol, Tobacco, Firearms and Explosives, all staffers must notify their supervisors if they are out of town.

"We have to know where everybody is," said ATF Assistant Director Michael R. Bouchard. "We are making sure we're ready and our best assets and equipment are available when we need them."

Members of the Washington area's Joint Terrorism Task Force plan to meet with other local and federal officials this week in Arlington to discuss potential election threats. Paul J. McNulty, the U.S. attorney in Alexandria, said the steps will include urging police to run the names of anyone they stop in coming weeks -- even for a traffic violation -- through the watch list at the FBI's Terrorism Screening Center in Crystal City.

"We want law enforcement to pay attention to small things and to suspicious things," McNulty said. "We want to get down to the foot patrol, the cop on the beat level, so when a police officer responds to something or sees something curious, that officer realizes it's especially important now to take the extra step to check it out."

New airport security procedures outlined earlier this month called for more discretion among screeners to pull passengers aside for additional scrutiny and new procedures that allow pat-downs with the front of the screener's hand to be able to detect hidden items. Those procedures were enacted in response to terrorist attacks on two Russian airliners last month, in which two Chechen women allegedly smuggled explosives on board, killing 90.

D.C. Police Chief Charles H. Ramsey said District police remain on increased vigilance and indicated that orders have not changed for officers since the warnings were received. These warning were separate from the August threat to financial centers in New York, Newark and Washington.

Staff writers Sara Kehaulani Goo, Sari Horwitz, John Mintz and Dana Priest in Washington; Jerry Markon in Alexandria; and correspondent Craig Whitlock in Berlin contributed to this report.