Business and civic leaders are welcoming the Comcast Corp. and Liberty Property Trust plans for a $1.2 billion office tower in Philadelphia's Center City. When it rises from the site at 18th and Arch the building will be among the tallest in the U.S.

Paul Levy, head of the Center City District, said the monumental plan is only partly about ego -- though some of the enthusiasm surrounding the communications giant's Wednesday announcement stems from rooting for the home team. But Levy said the 59-story tower signifies the company is making a major commitment to the city where it started.

"I hate to sound like an economist, but the difference between very important firms that just serve the local market and firms that import business from elsewhere is huge in terms of the economic impact," Levy said. "You'd have to go back to the Pennsylvania Railroad for a company of this scale, who's growing national market share, who's concentrating that energy and resources in Philadelphia."

After Comcast acquired NBC Universal in 2011, there was concern that the company could shift its resources to other locations.

A study by Econsult Corp., paid for by Comcast, estimates construction of the new tower will create 20,700 temporary jobs in Pennsylvania. When construction is completed, Comcast intends to move permanent jobs from elsewhere in the region and create new positions in Philadelphia.

Ironically, the area where the giant tower may have the least impact could be the real estate market, according to the president of the Greater Philadelphia Association of Realtors.

While it will add a million square feet of top class office space, since Comcast will be taking up most of the giant tower "it's not going to have a big dent in having more availability," said Alan Domb. "The big benefit I should mention is the jobs, construction, architectural, engineering that building a $1.2 million building brings to Philadelphia."

For that forecast economic benefit, the project will receive $40 million in city and state grants to extend the subway concourse and other infrastructure around the site. It's also eligible for a 10-year city tax abatement and an additional $4.5 million in state tax credits conditional on Comcast meeting job creation targets.

Liberty Trust and Comcast say the building will be complete by 2017.