Hundreds of police officers and federal agents will blanket the District this week to provide security as world leaders arrive for the first presidential funeral here in three decades and the first in the shadow of the 2001 terrorist attacks.

D.C. and U.S. Capitol police yesterday canceled days off, and the U.S. Department of Homeland Security announced that memorial services for former president Ronald Reagan would be a National Special Security Event -- a designation that brings with it heightened planning and resources.

"We are mobilizing the whole department," said Cmdr. Cathy Lanier, head of the D.C. police special operations division. "This is a major event. . . . In the current environment, there is a lot to think about."

Security will be especially tight at the Capitol, where as many as 100,000 mourners are expected to pay their respects to Reagan as his body lies in state Wednesday evening and Thursday.

The former president's funeral will be Friday at Washington National Cathedral, where services will be closed to the public amid a heavy police presence.

Reagan, the nation's 40th president, who served from 1981 to 1989, died Saturday at his home in Bel Air, Calif., after a lengthy battle with Alzheimer's disease.

His will be the first presidential funeral in Washington since Lyndon B. Johnson's in 1973. The only former president to die since then, Richard M. Nixon, had his funeral service and burial in California.

As a National Special Security Event, Reagan's memorial service will receive an increased presence of federal agents and police officers, with the U.S. Secret Service coordinating law enforcement activities. The same status has been granted to the Group of Eight summit this week in Georgia and the Republican and Democratic nominating conventions this summer.

Sharpshooters will be posted on rooftops, bomb-sniffing dogs will roam the crowds, and scores of officers will line motorcade and funeral procession routes, officials said. The heightened police presence will be apparent from the moment the plane carrying Reagan's casket touches down at Andrews Air Force Base in Prince George's County about 5 p.m. Wednesday, authorities said.

After a short ceremony at the base, the casket will proceed to the District in a lengthy motorcade. Police declined yesterday to say what route the procession will take from Andrews and said they have yet to settle on final details of the plan. However, police and transportation officials warned motorists to expect lengthy delays during rush hour Wednesday as roads are closed to accommodate the procession.

The motorcade will stop near the White House at Constitution Avenue and 16th Street NW, where Reagan's casket will be transferred from a hearse onto a horse-drawn caisson. Led by a lone drummer, the procession will then head down Pennsylvania Avenue to the Capitol, arriving about 6:50 p.m.

At the Capitol, officials will hold a military arrival ceremony that is expected to last until 8 p.m. Former presidents, members of Congress, diplomats and other dignitaries are expected to attend. During the arrival, the Capitol area will be closed to the public, officials said.

Police could not say yesterday when the public would be allowed to visit the Capitol Rotunda, where Reagan's body will lie in state.

"We are preparing as if the viewing will proceed from Wednesday evening to Friday morning," said U.S. Capitol Police Chief Terrance W. Gainer.

Gainer said those who want to view the closed casket will enter through the Capitol's West Front Terrace, facing the Mall. Visitors will have to go through a preliminary screening at the south side of the Capitol and will pass through a metal detector.

No cameras, food, large purses or backpacks will be permitted inside, Gainer said. Once inside, visitors will walk up the Grand Stairwell to the second floor and Reagan's casket. Gainer encouraged visitors to take Metro to the Union Station, Smithsonian or Capitol South stations.

Capitol Police officials began about 13 months ago to update a long-standing presidential funeral plan, which envisioned visitors entering the Capitol from the East Front. Construction at the East Front caused them to revise the plan yesterday.

Friday morning, Reagan's casket will be placed in a hearse. It will leave the Capitol in a motorcade at 10:45 a.m. and arrive at Washington National Cathedral about a half-hour later. The funeral is scheduled to begin at 11:30 a.m.

The cathedral has gone to "modified Level 3 security," which means security checkpoints have been set up at all access points to the cathedral's close, officials said.

"We have not had a funeral for a president here since Dwight Eisenhower's funeral" in 1969, said Gregory A. Rixon, the cathedral's director of public affairs. That service was held in a different building because the cathedral had not been completed.

The close -- the 57-acre area around the cathedral -- will be closed to cars later this week, as security efforts intensify, he said.

Rixon said the public will not be allowed on the cathedral grounds during the funeral. "This is a ticketed event," Rixon said. "The general public will be able to watch on television."

Services are expected to conclude about 1:15 p.m., and Reagan's body will return to Andrews Air Force Base in a motorcade for the return flight to California. The burial will be Friday evening at the Ronald Reagan Presidential Library in Simi Valley, Calif.

Preparations for Reagan's funeral have been in the planning stages since he took office in 1981, and the military has a 138-page book that covers even the smallest details of the event.

Despite the planning, authorities said they are still scrambling to work out the last kinks.

"It's going to be a pretty big, a very big event," said D.C. Police Chief Charles H. Ramsey. "You never know when you are going to have to put it into motion. It's a challenge, but we'll handle it."

Staff writer Steve Ginsburg contributed to this report.