PITTSBURGH - This city has become a hub for technology, medicine and higher education, but visitors still expect to see smoke- and fire-breathing steel mills when they emerge from the Fort Pitt Tunnel into downtown.

City leaders hope that changes tomorrow, when President Obama meets here with the heads of state from the world's industrialized nations and the European Union for the third Group of 20 leaders summit.

"We're looking at this as an opportunity to reintroduce the world to Pittsburgh - the new Pittsburgh, the Pittsburgh that is doing better than most and providing opportunities for folks," Mayor Luke Ravenstahl told reporters in Washington this month. "We really want to tell that story of that great turnaround the president keeps talking about when he talks about Pittsburgh."

Ever since White House Press Secretary Robert Gibbs announced in May (to the guffaws of the press corps) that Pittsburgh would be hosting the summit of world leaders, city officials have been preparing to seize the moment as if they were dusting off the parlor room for out-of-town visitors.

Ravenstahl led 600 volunteers in plucking old tires and greasy hamburger wrappers from the streets in a half-dozen city neighborhoods, and the Western Pennsylvania Conservancy is spending $152,000 planting small maple and magnolia trees and a multitude of flowers and shrubs near the David L. Lawrence Convention Center, where leaders are scheduled to meet Friday.

The Sports & Exhibition Authority, which owns the convention center, spent another $110,000 to give the iconic building its first major cleaning - with pressure washers and cases of Ajax - since it opened in 2001.

On the face of Mount Washington, the hillside overlooking the point where the Monongahela and Allegheny rivers form the Ohio River, Bayer Corp. covered its rusting sign with a 6,750-square-foot banner welcoming the summit.

Local officials have good reason to be excited, said Ron Maloney, founder of Dynamic Impact Consulting, an international business-advising company based in the city.

"Chances are, if someone knows something about Pittsburgh, they know where we've been," Maloney said. "What they need to know is where we're at now and where we're going."

The Pittsburgh summit could have a lasting legacy too, said Roger Cranville, president of GlobalPittsburgh, a group that promotes the region to international clients.

Finance ministers have been attending G-20 summits for a decade, but heads of state started coming only last year with a November gathering in Washington, and then again in London this spring.

Previous sessions focused on emergency responses to the financial crisis, but now leaders can start to address the underlying causes, Cranville said. Any solution that comes out of the meeting could become synonymous with the city.

"I'm hoping this will be known not as the G-20 summit but as the Pittsburgh summit," he said.

Security has been a major concern. Pittsburgh will bolster its force of 900 police officers with 3,100 officers from the state police, the National Guard and cities such as Philadelphia and New York.

During the summit, most car traffic will be prohibited from entering downtown, and police are coordinating rolling blockades along the highways as they ferry leaders to and from Pittsburgh International Airport, 19 miles west of the center city, and around to local sights.

Still, protesters could outnumber police by 10 to one if everyone who plans to demonstrate in the city shows up.

That list includes John Parker, of South Central Los Angeles, who rented an SUV last week, loaded it with four friends and drove across the country to Pittsburgh. He arrived Saturday and pitched his tent with a group called Bail Out the People, which plans several marches to demand jobs.

"We have to do it for our own survival," Parker said.

"It's like we have no choice. It's either be depressed and demoralized or fight back."