The Secret Service and D.C. police plan to erect roadblocks and screen pedestrians as far as three blocks from Pennsylvania Avenue in the tightest security cordon ever for a presidential inauguration, downtown businesspeople say.

Property owners, building tenants and private security officials said they have been told that vehicles will be barred from the blocks surrounding the historic avenue, which President Bush's motorcade will travel before he is sworn in at noon Jan. 20 at the U.S. Capitol and afterward when he leads a parade back to the White House.

The Secret Service, which is overseeing inauguration security, declined to comment yesterday. An announcement on the restrictions is expected next week. Privately, officials have met with those who do business along Pennsylvania Avenue as they prepare for the event. The plans are fluid and could change depending on the government's threat assessments.

Access to buildings in the area will be limited. Employees will have to present government-issued identification cards, hotel guests will be required to show their room keys, and others attending private inauguration parties must have their names submitted ahead of time to the Secret Service, several business owners and executives said.

Tens of thousands of paradegoers also will be screened and directed separately to viewing spots.

"Clearly, this is the first inauguration after September 11, 2001, and there have been significant changes in how we do things," said Harold F. Nelson, president of the Apartment and Office Building Association of Metropolitan Washington. He praised security agencies for imposing unprecedented safeguards in cooperation with hotels, property managers and businesses.

"To make this as palatable and comfortable for everyone, the Secret Service truly did reach out early," said Nelson, vice president of CarrAmerica, which owns 10 buildings near the parade route.

The pomp and pageantry of Inauguration Day has long been accompanied by tight security, such as the posting of snipers on rooftops and the sealing of windows on buildings facing Pennsylvania Avenue. Yetpreparations this time far exceed those for George W. Bush's first inauguration four years ago.

Security officials have refined practices used to defend against car or truck bombs and have improved their ability to screen people as they ratcheted up security at a series of major events since the 2001 terrorist attacks, such as the funeral last year for former president Ronald Reagan, meetings of the World Bank and International Monetary Fund and the presidential nominating conventions in New York City and Boston.

Dozens of high-rise owners in the downtown area have been contacted by the Secret Service since November and asked to complete security surveys, prepare contingency plans and meet specific requirements for their entrances, garages and roof decks.

Caterers have been ordered to truck supplies into place the night before the inauguration because all vehicles will be prohibited Jan. 20.

Two Secret Service and police perimeters will be set up to move people out of their vehicles and on foot where they can be screened, sometimes more than once. Two Metro stations, Archives-Navy Memorial on the Yellow and Green lines and Smithsonian on the Blue Line, will be shut on inauguration day until after the parade. Federal buildings will be closed, most private deliveries halted and garages facing the avenue sealed.

Organizers of private parties expecting more than 100 guests -- of which there are scores among the law firms, consultancies and trade groups in the pricey real estate that lines the avenue -- have gone through special checks, often to the inconvenience of those attending the posh events.

At least one law firm said it would scale back plans because of the heightened security.

The Washington-based law firm of Crowell & Moring LLP has hosted four inaugural parties at its 1001 Pennsylvania Ave. NW offices. The parties, with a balcony view of the parade route, have been formal, catered affairs with up to 600 guests from around the country and the world.

But this time, the firm is throwing a smaller, more subdued party for about 250 guests, many of them local. The heightened security is "perhaps the determining factor in why we're scaling back," said Jose Cunningham, chief marketing and business development officer.

The firm sent out invitations to its previous inaugural parties but this year is asking lawyers to invite clients personally. Only one entrance to the building on E Street NW will be accessible to guests, the building garage will be sealed the night before, and Secret Service agents will be at the party, Cunningham said.

The Department of Homeland Security has scheduled a public announcement about inauguration security for Tuesday, with briefings for businesses to follow Wednesday and Thursday.

Del. Eleanor Holmes Norton (D-D.C.), who has condemned the fortification of Washington over the past three years and unilateral street closures by federal agencies, said inaugural preparations should not be excessive.

"I am concerned that we are unnecessarily closing large parts of the city," said Norton, who will meet with federal planners today. "I want to go down each and every one of these issues, to see if we can get the greatest amount of openness . . . [and] an ironclad security reason for each and every closing."