For Lower Manhattan, the coming years are poised to be some of the most vibrant in history, as a strong financial sector, a booming residential population, and progress at ground zero are creating a dynamic climate for businesses and residents.

Still, a possible economic slowdown and the potential departure of a key corporation loom as significant challenges to the area, which has slowly been finding its footing in the six years since the terrorist attacks of September 11, 2001.

As Lower Manhattan gets consumed by preparations for the sixth anniversary — the Port Authority held a press briefing about construction efforts yesterday and the developer of Towers 2, 3 and 4, Silverstein Properties, will unveil updated designs of its skyscrapers today — the area has moved past some of the large, unresolved obstacles it faced in years past.

Gone is much of the uncertainty about the development at ground zero, as over the past 18 months an accord on construction was reached, an agreement was met with insurance companies to pay out hundreds of millions of dollars, and the Port Authority is slated to hand over the eastern portion of the site to Silverstein Properties by the end of the year.

The allure of the area to the financial industry was ratified by a commitment by JPMorgan Chase in June to build its investment banking headquarters on the site of the former Deutsche Bank building, a move that comes as office vacancies have hit their lowest point in years.

“You look around downtown; you see cranes everywhere,” Deputy Mayor Daniel Doctoroff told The New York Sun. “It’s really quite gratifying to see when plans — especially complicated, multipart plans that reflect a completely different vision of the future — come together more or less as you’d hoped.”

Adding to the success of downtown’s commercial market is the growing residential population, as the increasing demand for housing has engendered office conversions and new apartment towers in the historically single-use area. With the added diversity of uses — the growing residential population has inspired a burgeoning retail market — officials and business leaders say the area is on far more stable ground than in years past, and revitalization efforts would be difficult to derail, even by an economic downturn.

“What’s really happened in the last couple of years is that Lower Manhattan has become a magnet both to live and to work that is not based strictly on price points, or based strictly on patriotism,” the president of downtown landowner Trinity Real Estate, Carl Weisbrod, said. “The attractiveness of Lower Manhattan and the live-work environment that’s been created here has really made it resilient.”

While downtown’s outlook today is marked by its optimism, an escalation of the credit crunch or another external factor could throw a wrench into the local economy, especially given its heavy reliance on the financial industry.

“The biggest threat is always major changes in national policy that could damage the economy,” the CEO of the Partnership for New York City, Kathryn Wylde, said. “If that happened at any scale, that could be a problem for the office market.”

A move by Merrill Lynch, which is said to be contemplating a relocation to Midtown from its existing site downtown, would also serve as a blow for the area.

The Port Authority and Silverstein Prosperities still have a tall task ahead of them to find tenants at the World Trade Center site towers. Their ability to fill the skyscrapers with companies paying reasonable rents depends in part on the whims of the broader economy, real estate experts say, and failing to do so would undoubtedly have a damping effect on Lower Manhattan’s comeback.

“Sure, nobody can forecast what the market will look like in a year or two when this building is really ready to go to market,” Port Authority executive director Anthony Shorris said yesterday, adding: “There’s a lot of evidence that there’s very strong market demand for World Trade Center property.”