From the swearing-in ceremony for President Bush at the Capitol on Jan. 20 to the presidential parade review at the White House to the evening galas, the inaugural events will be the first in decades to be held in wartime and the first since the terrorist attacks of 2001. They will take place at buildings that symbolize American democracy, and hundreds of thousands of people are expected to attend, including the highest-ranking government officials, other prominent Americans and dignitaries from around the world. It is hard to imagine, say security experts, a bigger target for terrorists.

"This is a very, very serious event," said James J. Varey, a retired Secret Service officer and former chief of the United States Capitol Police who worked on security plans for every inauguration from 1973 to 2001. "The public has every right to be concerned if we've done enough and covered all of our bases."

Since President Ronald Reagan's second inauguration, in 1985, nearly four years after he was shot in an assassination attempt, security efforts have steadily intensified.

In January 2001, when the country was divided over a disputed presidential election, the newest development was security checkpoints along the parade route on Pennsylvania Avenue, from the Capitol to the White House, to minimize the ability of protesters to disrupt the procession. None did, although several people threw eggs and debris at Mr. Bush's limousine as it left the Capitol grounds.

But Mr. Bush's second inauguration is vastly different from his first, with many Americans fearful of another terrorist attack. The atmosphere has prompted officials to devise a detailed security plan that they are reluctant to discuss. Security personnel involved with planning the events, in agencies like the Secret Service, the F.B.I. and the Joint Forces Headquarters for the National Capital Region, declined to disclose any details.

But all promised that the efforts would surpass those of the past, building on tactics used at the 2001 inauguration and taking into account the symbolic importance of the day as well as its potential as a target for terrorists.

"We're mindful of world events, and we adapt as necessary," said Lorie Lewis, a spokeswoman for the Secret Service, the lead agency in developing the security plan. "We are prepared to handle any potential situation that may arise during this. We're also prepared to respond tactically to any situation."

Many of the resources that will protect the inauguration have been in place since the Sept. 11 attacks and the discovery of anthrax in Congressional offices weeks later. Anti-aircraft weapons sit atop a federal building near the White House. Monitors have been installed around the city to measure for airborne radiological, chemical or biological substances. The Capitol Police force has grown by several hundred officers to more than 1,500, a record number, and many of them now carry M-16 rifles.

But security officials said safeguards for next month's events would involve more equipment and people than in 2001, including larger numbers of troops and uniformed and plainclothes officers. Besides the armed soldiers who will be deployed around the city, 4,000 others who routinely serve the capital region will be on call.

"It's not like we're going from zero to full blast," said Chief Terrance W. Gainer of the Capitol Police. "This reflects a continual, gradual buildup with substantially more coordination, more personnel, more technology and greater sharing of intelligence."

Not all involved with security efforts will have specialized assignments, like standing on rooftops along the parade route with binoculars and high-powered rifles. Many will draw more routine duties, such as operating pedestrian checkpoints on streets leading to Pennsylvania Avenue and mingling in crowds to watch for potential disruptions.

Beyond increasing personnel, said Mr. Varey, who was part of President Reagan's security detail on the day he was shot in 1981, inauguration planners are also using public awareness as a tool.

"This time," he said of planners, "they have made an appeal to the public to be the eyes and ears of security to get the public involved in security on a greater scale than I've ever seen."

While terrorist activities are the prime concern, protests are also being addressed in security plans. Several groups say they intend to stage peaceful demonstrations, but political protests sometimes grow violent, as they did at world trade meetings in recent years in Seattle, Miami and Washington.

Brian Becker, national coordinator for the Answer Coalition, an antiwar and antiracism group, said he expected thousands of protesters to line the parade route "in a legal, spirited, peaceful demonstration," carrying signs calling for the withdrawal of United States troops from Iraq and for Mr. Bush's impeachment.

Another group is planning a protest in which participants would turn their backs to Mr. Bush's limousine as his motorcade passes. Jim McDonald, an organizer, said the action's effectiveness would depend on how close to the barricades the protesters could get.

Both organizers worried that security would be so intense and access so difficult that their groups' messages would be muffled.

The Bush administration, Mr. McDonald said, "is using national security as a pretext to stifle dissent and to marginalize dissenters."

"They're not dissuading Osama bin Laden," he added. "They're dissuading protesters from coming out by creating a climate of fear."

Representative Eleanor Holmes Norton, a Democrat and the District of Columbia's delegate to Congress, is working closely with the agencies planning the inauguration and said she was satisfied that security would be strong enough to discourage a terrorist attack. "And terrorists know it," Ms. Norton said. "Besides, they like the element of surprise."

She said she worried more about the permanent changes on Capitol Hill and elsewhere, giving the city a militaristic feel that is amplified by the expanded presence of security personnel at important events like an inauguration.

"People with guns are on rooftops right now," Ms. Norton said. "Surveillance cameras are everywhere. You have to do everything you can, and I am willing to abide a lot of extra security for the inauguration. But I just don't think President Bush wants the city to look more like a military show than a celebration."