President Clinton can thank one of his heroes, John F. Kennedy, for the renaissance he'll see Monday along Pennsylvania Avenue while parading down the historic street to the White House.

Yet Clinton could be remembered as the president who undermined the revival of the nation's Main Street by closing a two-block section in front of the White House.

During Kennedy's inaugural parade in 1961, the president "waved to the left, waved to the right and there was nothing there. The city was moving out Wisconsin Avenue, out Connecticut Avenue," recalled Sen. Daniel Patrick Moynihan (D-N.Y.), then a Labor Department official. Kennedy tapped Moynihan to help start a public-private makeover of 21 blocks of Pennsylvania Avenue that is nearly finished and has added millions of square feet of office, arts and retail space as well as hundreds of hotel rooms, apartments and condominiums.

"You hear constantly that everything is falling down" in the District, Moynihan said. "Well, this ain't."

But travel along the restored corridor has become more difficult after Clinton's May 1995 decision to shut vehicle access to Pennsylvania in front of the White House. The move divided downtown Washington between east and west, making trips across the city tougher at a crucial time for downtown revitalization.

Business, political and civic leaders are putting together a plan to energize the city's core with the MCI Center sports arena, a new convention center, an opera house, museums and more entertainment retailers.

"The mission for a `living downtown,' one that is active 18 hours a day, will be severely curtailed if one of the main arteries leading from the west side of the city is closed," said Herbert S. Miller, a developer who headed a blue ribbon task force on downtown revitalization. "This situation cannot be viewed as a positive incentive for businesses to locate downtown."

A month after a truck bomb blew up a federal office building in Oklahoma City, killing 168 people, Clinton ordered the section of Pennsylvania closed, based on classified reports that said the White House was vulnerable to a truck bomb. The street will be opened only for ceremonial functions, such as Monday's parade.

"Here they're going to open up Pennsylvania Avenue so they can have a party," groused Thomas W. Wilbur, president of the D.C. Building Industry Association, which represents builders, developers and the real estate industry. "They have their party, and the next day all the rest of us who live and work here have to live with this problem."

Clinton, echoing assessments of others in and out of the administration who studied the truck bombing threat, has said the Secret Service's arguments were persuasive, although independent bombing experts say the White House may be far enough from the street to withstand an explosion. Clinton isn't planning to change his mind, and the National Park Service is working on a permanent redesign of the two-block area. A future president could always reverse course; Clinton's challenger, Robert J. Dole, said he would have reopened Pennsylvania to vehicles.

The closing of Pennsylvania, and westbound E Street, forced 38,000 vehicles a day onto other routes, clogging D, H, I, K and L streets. Constitution Avenue traffic jumped 50 percent after the closing. Commuting, taxi and shopping trips were lengthened, and it takes longer for emergency vehicles to cross the city.

Many people simply have stopped driving between east and west of the White House. That doesn't make restaurants happy; a cab ride from a location east of the White House such as the Reagan building to restaurants on the west side, such as Maison Blanche at 17th and F, takes up most of a lunch hour.

Before Clinton's decision, downtown was a single area, including both sides of Pennsylvania Avenue and tying in the Georgetown-West End and Capitol Hill neighborhoods.

"Like the Berlin Wall of the Cold War era, we now have two separate districts, two separate cities: East Washington and West Washington," said Christopher Reutershan, of Concord Partners, a real estate development services company. "We're seeing an increasing divide developing."

In effect, Clinton unwittingly has redrawn the geography of downtown Washington.

Until the 1980s, Washington's central business district was a so-called golden triangle bounded by K Street, New Hampshire Avenue, Massachusetts Avenue and 16th Street. Some business leaders now call that area West Washington.

In the 1980s, the definition of the business district changed to include the eastern part of Pennsylvania, an area also bounded by 15th Street, Massachusetts Avenue and E Street. That part of Pennsylvania was redone by the Pennsylvania Avenue Development Corp., a small federal agency started during the Nixon administration but conceived by a Kennedy administration panel that included Moynihan.

The agency spent 25 years and $1.5 billion in private money converting the seedy mile between the Capitol and the Treasury Department into the current grand boulevard of hotels, theaters, memorials, embassies, shops, restaurants, offices and residences.

Half of the city's 50 largest law firms have moved to East Washington, including the five largest.

Moynihan, perched on a fourth-floor balcony of Market Square overlooking Pennsylvania Avenue, pointed out the changes to the thoroughfare since Clinton's first inaugural parade in 1993.

Six classy, diverse restaurants have opened, though the 69-year-old Moynihan admits having "absolutely no idea" what Planet Hollywood is. The mammoth Ronald Reagan federal office building and international trade center at 14th Street and Pennsylvania Avenue, a giant hole in the ground four years ago, is almost done and the beat-up intersection there repaved.

Work has started on a fourth building similar to Market Square, where Moynihan lives, that will include residences, offices, shops and restaurants. Although there are plans to spruce up other buildings, including the old District Building, the remaking of Pennsylvania is nearly finished.

Clinton's interest in helping the city in other ways -- including a proposal to have the federal government take over billions of dollars in District programs in exchange for dropping the federal payment to the city -- prompted Wilbur to offer a suggestion.

"One low-cost way he could contribute to the recovery of the city is to reopen Pennsylvania Avenue," Wilbur said. "It would be a great gesture to the city that the White House realizes our plight."

Then again, Moynihan said, the federal government could build an underpass to carry Pennsylvania Avenue traffic underneath, with a pedestrian plaza on top. Closing the road -- and putting barriers around the Capitol -- gives the impression the United States is beleaguered, he said, which is why he did not agree with those decisions.

"We can do what is necessary for security at the White House without declaring us to be a nation under siege," he said.

Staff writer Maryann Haggerty contributed to this report.