An unprecedented level of security will frame President Bush's second inauguration, with officials planning to use thousands of police from across the country, new screening technology for inaugural guests and a military contingent that could include a combat brigade of up to 4,000 troops.

Security is always tight on Inauguration Day, but it will be magnified for the first inauguration since the Sept. 11, 2001, terrorist attacks. Law enforcement officials have been preparing for months to protect U.S. and world leaders and citizens who attend.

Organizers are planning a traditional inauguration capped by a parade down Pennsylvania Avenue and the usual evening balls. Bush has yet to name his inauguration committee, which will oversee planning of the pageantry and festivities, but law enforcement agencies are in high gear.

As tens of thousands of people come to Washington to watch the Jan. 20 swearing in, the city will be filled with military personnel, FBI agents in full SWAT outfitting, snipers on rooftops and scores of bomb-detecting dogs. The region's air defenses have been strengthened to prevent intruder aircraft, and sensors will be deployed throughout the area to detect biological, chemical or radiological material.

About 2,000 out-of-town officers will help with security and traffic details. Undercover officers will work the crowds, and D.C. police officers will be posted every six to eight feet along the parade route.

Plans call for sturdier barriers and more checkpoints and metal detectors along the parade route than in previous years. Officials also are setting up a higher-security ticketing and credentialing system for some events, to prevent people from using counterfeit materials to get into the balls and more restricted areas.

"There will be far more security and more police than four years ago," said Terrance W. Gainer, chief of the U.S. Capitol Police, the agency charged with protecting the Capitol, where Bush will be sworn in. "Everything has changed since 9/11, so there is a different context in which this inauguration is being planned."

Law enforcement authorities do not have specific information that al Qaeda or another terrorist group is targeting the inauguration. But the events will attract political leaders from throughout the country and the world and will be staged outside symbols of American democracy, officials said.

"The inaugural is a rich, symbolic, highly visible target," said Jim Rice, the FBI supervisory special agent who overseas the National Capital Response Squad. Rice's squad works closely with the Joint Terrorism Task Force in the FBI's Washington field office to monitor and respond to terrorist threats.

This will be the first inauguration since creation of the Homeland Security Department, which also is a central part of the security planning.

The Secret Service is the lead agency for the inauguration because the ceremony and celebrations are considered a National Special Security Event, a designation that brings with it heightened federal planning and resources.

Officials said the inauguration will be the culmination of a series of high-security events, including the summer political conventions, the Sea Island, Ga., summit of leaders from industrialized nations in June and the funeral in Washington that month of former president Ronald Reagan.

In Northern Virginia, a temporary joint command center is being set up in a federal facility. It will include representatives from other law enforcement agencies, including the D.C. police department, U.S. Park Police, Capitol Police and the FBI.

In addition, officials said the new Joint Forces Headquarters-National Capital Region is prepared to pre-deploy 4,000 active-duty combat forces in the District -- a significant departure from past inaugurations.

The military will support civilian authorities, if needed, and officials said they plan to project a much more forceful image than since at least the time of the Vietnam War.

About 2,000 troops, including members of the 82nd Airborne Division, were flown into Washington for Richard M. Nixon's inauguration in 1969, and some were stationed along the parade route. The military also helped protect the parade route for Nixon's second inauguration, in 1973. In recent decades, uniformed guards have played a mostly ceremonial role and specialized response teams stayed backstage.

In addition, the Military District of Washington Engineer Company, which specializes in extracting survivors from building collapses, and the Marine Corps Chemical Biological Incident Response Force will be on alert in the area.

A maritime security force led by the Coast Guard will include FBI and Department of Energy personnel on boats in the Potomac and Anacostia rivers to guard approaches to the city. Similar details were in place for Reagan's funeral.

"The major message is we are a hard target. We're not just sitting and waiting for something to happen," said Army Maj. Gen. Galen B. Jackman, commanding general of Joint Forces Headquarters-National Capital Region and the Military District of Washington.

For months, units in the command have conducted exercises to prepare for the inauguration, mapping staging areas, routes to rescue sites and emergency procedures from its Fort McNair headquarters. The exercises have contemplated a wide range of potential terrorist incidents, including suicide bombs, truck bombs and chemical releases.

"We will respond with the capabilities necessary to accomplish the mission," said Navy Rear Adm. Jan Gaudio, Jackman's deputy commander.

Authorities are building upon other security measures that have been employed for recent inaugurations. These steps have included inspecting miles of underground Metro and sewer tunnels, sealing manhole covers, closing streets and surveying the more than 450 downtown buildings with at least a partial view of the parade route.

D.C. police officials said they have requested help from scores of police departments east of the Mississippi River. Police Chief Charles H. Ramsey said he expects to need 1,600 to 2,500 officers from other jurisdictions.

In 2001, about 1,200 officers from other area departments helped secure the inauguration and balls, D.C. police officials said. At the time, police were mostly concerned about containing angry demonstrators who were protesting the results of the contested 2000 election. Police reported a few arrests and some vandalism.

Demonstrations are likely to be a concern of police this time. Organizers said they will bring thousands into the city again to protest Bush's second inauguration.

International ANSWER, the antiwar, anti-racism coalition that has sponsored some of Washington's biggest demonstrations against the war in Iraq, has been planning a counter-inauguration rally for months.

Another antiwar coalition, United for Peace and Justice, which organized a massive demonstration outside the Republican National Convention in New York in August, is discussing possible actions in Washington and elsewhere. The purpose, spokesman Bill Dobbs said, would be "to keep the heat on the Bush administration about the occupation of Iraq."

Ramsey said police expect the inaugural parade to follow its traditional route and pass a reviewing stand along Pennsylvania Avenue NW on the north side of the White House. That portion of the street has been closed to vehicle traffic since 1995, and planners said they expect security and design work to be completed in time for Bush's swearing in.

Officials said that none of the security measures is meant to keep people from attending the parade or other events.

"Our goal is to provide as safe an environment as possible, so America can enjoy one of its greatest celebrations, which is the inaugural celebration for the president of the United States," said Homeland Security Department spokesman Brian Roehrkasse.

Staff writers Manny Fernandez and Del Quentin Wilber contributed to this report.

Organizers are planning to follow the traditional parade route that was used in President Bush's first inauguration, but security will be heightened.