NEW YORK – With its huge reflecting pools, ringed by waterfalls and skyscrapers and a cavernous underground museum still under construction, the National Sept. 11 Memorial and Museum at the World Trade Center is an awesome spectacle that moved and inspired 4.5 million visitors in its first year.

But all that eye-welling magnificence comes with a jaw-dropping price tag. The foundation that runs the memorial estimates that when the roughly $700 million project is complete, the memorial and museum will together cost $60 million a year to operate.

The anticipated cost has bothered some critics and raised concerns even among the memorial’s allies that the budget may be unsustainable without a hefty government subsidy.

By comparison, the National Park Service budgeted $8.4 million this year to operate and maintain Gettysburg National Military Park and $3.6 million for the monument that includes the USS Arizona Memorial at Pearl Harbor. Running Arlington National Cemetery, which has more than 14,000 graves and receives 4 million visitors a year, costs $45 million annually.

Officials at the 9/11 memorial say they face unique challenges that make comparisons to other national memorials difficult. The foundation plans to spend at least a fifth of its operating budget, or about $12 million per year, on private security because of terrorism fears. Visitors to the memorial plaza pass through airport-like security, and armed guards patrol the grounds.

“The fact of the matter is that this was a place that was attacked twice,” said Joseph Daniels, the foundation’s president and chief executive.

Just operating the two massive fountains that mark the spots where the twin towers once stood will cost $4.5 million to $5 million annually, said the foundation’s spokesman, Michael Frazier.

Foundation officials didn’t respond to requests for information about other costs at the site, including the anticipated expense of running the museum, which is still unfinished and might not be anytime soon.

The museum was supposed to open this month, but construction all but ceased a year ago because of a funding squabble between the foundation and the Port Authority of New York and New Jersey, which owns the land the memorial sits on.

Daniels said it will take at least a year for the museum to open after construction resumes, meaning the site may not be fully complete until at least 2014. The failure to open the museum on time has thrown off the foundation’s financial planning. Officials had expected to use the museum, being built mostly with money from various government agencies, plus private donations, as its main source of revenue.

While visitors will be allowed into the above-ground portions of the memorial for free, the foundation plans to charge people to descend into the museum’s exhibition space, where they will see portraits of the nearly 3,000 victims, hear oral histories of the tragedy and view artifacts such as the staircase World Trade Center workers used to flee on 9/11.