Its retractable, igloo-shaped roof is the main reason historic preservation groups don't want Mellon Arena to be razed, even if the Pittsburgh Penguins waddle across the street to build a new nest.

But city officials and others say what was an architectural marvel when it opened in 1961 -- a 420-foot clear span dome, three times larger than the dome at St. Peter's Basilica in Rome -- is a monument to failed urban renewal that only can be fixed only if the arena is torn down.

"That land has become the most valuable real estate in the city, because of its proximity to major arteries," said City Councilman Sala Udin, referring to Interstates 279, 376 and 579, all within a block of the arena.

"It makes absolutely no sense to block development of that land to save a second arena next to a new arena," Udin said.

Mellon Arena's fate became an issue when the Penguins, the building's main tenant, detailed plans earlier this year for a new $225 million hockey rink across Centre Avenue on the site of a former hospital.

To help sell the plan to city, state and county officials -- from whom the Penguins want unspecified dollars -- the team suggested building a hotel, offices, shops and homes to generate tax revenues from the 20 acres now occupied by Mellon Arena and its parking lots.

In an ironic twist, historical groups attacked the plan even as city officials lauded it as a way to repair the city's historic Hill District neighborhood that was ripped asunder by the arena.

Udin was 10 years old when his family -- and about 8,000 other residents of the predominantly black neighborhood -- were herded into public housing in the 1950s to make room for what was originally known as the Civic Arena.

Built for $18 million, the arena's retractable roof was meant to make the facility an all-weather home for the city's Civic Light Opera, which suffered frequent rainouts while based at Pitt Stadium in the late 1950s. The venue proved to be too windy with the roof open, however, and the acoustics didn't meet light opera standards when the 2,950-ton stainless steel roof was closed.

Still, "it was the state of the art. If anything, it really set the goal for future stadiums of this sort," said Edward Laing, a structural engineer for Ammann & Whitney of New York City, who helped design the roof.

"It's only in the last 20 years that we're back to the hard, movable domes, instead of the fabric. It does have a unique position in engineering history," Laing said.

But the roof has become more of a novelty than a necessity -- especially since the National Hockey League's expansion Penguins arrived in 1967. In recent years, the roof hasn't been opened, because that can't be accomplished without disconnecting a large video display scoreboard the Penguins installed.

Robert Pfaffman is an architect with Preservation Pittsburgh, a group pushing to designate the building a historic site. That means the building couldn't be torn down -- or its outside changed -- without approval of the city's Historic Review Commission.

Pfaffman prefers renovating the arena for the Penguins, which the team has said is not feasible. Failing that, he wants to find another use for the arena, which he equates to the St. Louis Arch or Seattle's Space Needle.

He envisions a hotel within the partially opened dome, which he says could be glassed in to also house shops, restaurants and clubs.

"It's premature to dismiss it out of hand and say it can't work," Pfaffman said. "We're not just bookworms with our noses stuck in history books -- we're people who are really looking at this seeking a hip reuse of the building."

Susan Golomb, director of the city Planning Department, says the historic designation isn't needed to save the building and "cuts off other options" in redeveloping the site.

S. Philip Hundley, a principle in DRS Architects, the successor to the company that designed the arena, hopes it will survive.

"We're very happy to tear down buildings and put new ones on top of them, but as we're growing older, we're preserving more things," Hundley said. "You really couldn't build a building like that today, and you already have one. So why get rid of it?"