A $90 million picture at the Philadelphia Museum of Art was finished today when an eager public walked through the front door of the museum's first new exhibition building since the main structure opened eight decades ago.

About 100 visitors gathered at the steps of the Ruth and Raymond G. Perelman Building on a cool morning as museum director Anne d'Harnoncourt, chairman H.F. "Gerry" Lenfest, stealth arts leader Marjorie O. "Midge" Rendell and other dignitaries cut a large red ribbon and welcomed art lovers up the steps.

"We knew the building could not be complete until the public claimed it as its own, and that is the joy of today," said d'Harnoncourt before she herself walked into the building and her eyes welled with tears.

It was less a day for throngs than quiet contemplation of art; the center spine of the Perelman, a skylit galleria lined with sculpture, rarely hosted more than a dozen visitors at a time.

But those who did turn up were audibly wowed, offering security guards impromptu reviews of the art and the space, and releasing exclamations as they turned the corner into the sunny central arcade.

"Oh my God, it's beautiful. The exterior is gorgeous. The hall filled with light is exquisite," said Lucinda Trask, a Port Richmond costume designer who came to study the collections of fashion designers James Galanos, Gustave Tassell and Ralph Rucci.

Construction workers, infants rolled about by their grandparents, a couple of medical students, a drawing collector from New York - everyone looked delighted by the 173,000-square-foot addition.

The building's namesake smiled at the sight of people sitting in the cafe, passing in front of photos by Alfred Stieglitz and examining spaces designed by New York architect Richard Gluckman.

"It's fantastic. Everyone just raves about it," said Raymond Perelman, who along with his wife, Ruth, gave $15 million toward the project.

He also admired something else he gave - or at least loaned - for the opening.

"This was in my living room," he said, pointing to Aristide Maillol's bronze of a woman of ample proportions. "Anne [d'Harnoncourt] said it would look better in here."

And does it?

"I guess so," he said. "Look at how high that ceiling is. My living room is high, but not like this."

For her part, d'Harnoncourt's impromptu arias about the building's potential could hardly be contained. She stood in the building's foyer, accepting compliments and talking art.

A museum volunteer wanted to know what the significance of the snake was in the Anselm Kiefer sculpture. "He's always someone who mingles the hopeful, aspirational and the dangerous," said d'Harnoncourt. "Snakes are something to look out for."

A photography buff suggested a lecture series. Funny you should mention it, d'Harnoncourt said. "That could happen in our new media room."

The Perelman's content and programming will be explored over time, with plans for exhibitions of new acquisitions, and also the possibility of films and concerts. The art now in the building - the 1955 silk cocktail dresses, Stieglitz cityscapes and soulful portraits of Georgia O'Keefe, the Russel Wright "flair" tumblers in the modern and contemporary design gallery - will constantly change. Exhibitions will turn over, on average, every six months.

That means visitors must come back again and again to see what's new, giving the museum the hope of luring about 80,000 visitors to the new building in the first year. That's on top of the 750,000 to one million who already see the Impressionist masterpieces, Duchamps and arms and armor in the main building every year.

Actually, today's opening was only one of many in the last several months. Members were admitted last week. Donors and potential donors have donned construction hats and taken tours for more than a year as museum leaders have struggled to close the $20 million to $25 million funding gap to cover the $90 million spent on acquisition of the building and renovations. Only last week, at a gala for philanthropists and other VIPs, a couple pledged $1.5 million.

Other opening events are planned for area artists and cultural leaders; teachers, who will learn about the new education center at a back-to-school night; and corporate donors, who get a fete to themselves.

Eventually, the Art Museum hopes to capitalize on visitorship to the Barnes Foundation, whose collection could end up on the Parkway if civic leaders get their way. From the Perelman by brisk walk, a Barnes on the site of the Youth Study Center would be about 13 minutes away.

In the meantime, there's a better lure to the Perelman. A $500,000 grant from Wachovia to the museum will underwrite admission.

For today's visitors and anyone wanting to see a David Smith sculpture, Philippe Starck juicer or sleek 1968 Gustave Tassell wool coat before the end of the year, that means admission is free.

Contact culture writer Peter Dobrin at 215-854-5611 or pdobrin@phillynews.com.

Read his blog at http://go.philly.com/artswatch.