Many people are looking forward to March 2011 - the anticipated opening of the expanded Convention Center - and none more than those already selling the yet-to-be-completed meeting, exhibit, and ballroom spaces.

With $1.8 billion in convention business already booked for the larger complex, yesterday was the official halfway point of the $786 million project.

Once completed, it will give Philadelphia a major-league convention center.

"It allows us to attract groups that we couldn't in the past because we weren't big enough," said Ahmeenah Young, president and chief executive officer of the Pennsylvania Convention Center Authority.

That means attracting larger national conventions, especially health and medical groups, and accommodating multiple conventions at the same time, Young said.

Senior executives of the authority yesterday gave a tour of the massive construction zone between Broad and 13th Streets - an eye-catching development for commuters and passersby for more than a year.

At this point in the construction, all that can be seen from the interior are the foundation and concrete columns. The spaces are wondrous, however, the equivalent of 10 football fields.

The Pennsylvania legislature and Gov. Rendell agreed to use gross revenue from the state's casinos to pay for most of the expansion. A portion of the hotel tax increase that took effect this year will also fund the development.

Jack Ferguson, executive vice president of the Philadelphia Convention and Visitors Bureau, which books the Convention Center, said the additional one million square feet of sellable space would allow "two of everything" - two citywide conventions, two trade shows, or two large meeting groups at the same time.

"We could have one on the Market-Arch Streets side and the other one on the Broad Street side without either one interrupting the other's program," he said yesterday before boarding a flight to Indianapolis to sell the Convention Center to an educational group there. "The expansion gives the building great flexibility."

The completed building will cover the area between Arch, Race, 11th and Broad Streets, besides its existing wing over the Reading Terminal Market. It will house the largest ballroom on the East Coast and 541,000 square feet of exhibit space on one level, roughly matching the size of the convention center in Washington. The building will be the 14th-largest convention center in the nation, larger than even New York's and Boston's.

The 376,000-square-foot addition was originally to be completed in late 2010. Ferguson said the city had lost more than $400 million in business because of the delay as groups were told to book in other cities.

The soft economy continues to be a drag on convention business. Travel for meetings and conventions this year is expected to decline 9.2 percent in volume and 12.9 percent in spending from 2008, according to U.S. Travel Association estimates.

Meanwhile, the exhibition industry experienced a decline of 11.6 percent for the first quarter this year compared with the same period in 2008, according to the Center for Exhibition Industry Research, a trade group in Dallas.

Thus, a timely opening is imperative for the larger building here.

Jennafer Ross, president of Philadelphia Area Meeting Professionals International, said she and her peers were already selling the 23 additional meeting rooms and extra 123,000 square feet of meeting and banquet space.

Bill Walsh, general manager of the 1,408-room Philadelphia Marriott at 1201 Market St., said city hotels would be able to host a citywide convention (requiring at least 2,000 rooms) during big shows, such as the Philadelphia Flower Show or the Philadelphia International Auto Show. That was not possible with the existing center.

"The additional revenue we will see from the expanded Convention Center will improve hotels' financial performance through increased room nights," he said, "and, more importantly, it will add much needed jobs for Philadelphians."

Contact staff writer Suzette Parmley at 215-854-2594 or sparmley@phillynews.com.