Overcoming enervating heat, more tourists and conventioneers are traipsing to Philadelphia museums and sites this summer than last, more are attending major exhibitions, and more are staying overnight in hotels, according to tourism officials and spot checks at key institutions.

The increases may be modest overall, officials say, but the gains are real. At the Philadelphia Museum of Art, the newly opened Barnes Foundation, the just-reopened Rodin Museum, the Franklin Institute, the National Constitution Center, and the Independence Visitor Center, numbers are strong.

The Barnes Foundation has welcomed more people in its first two months on the Benjamin Franklin Parkway - 67,435 - than it did in all of 2009 in Merion, according to Derek Gillman, Barnes president and chief executive.

Visitors to Independence National Historical Park, however, still the region's major visitor attraction, are off overall for May and June.

In June, the park had 375,600 visitors, down from 438,192 in June of 2011, according to Jane Cowley, park spokeswoman. May 2012 was also down compared with May 2011.

Cowley said the declines "may well be due to the heat wave we have been experiencing."

Overall, park visitation is off slightly to 1.70 million this year, compared with 1.71 million through June of 2011.

This is not the case at the Independence Visitor Center across the street from the Liberty Bell Center and the President's House memorial site, Sixth and Market Streets.

"We're having what I'd call a really good year," said James Cuorato, president and chief executive of the visitor center. "The first quarter was up significantly for our building. I didn't think we'd be able to sustain that. But through the Fourth [of July] we're up 6 percent from last year."

Cuorato said visitation to the center, an independent nonprofit operation, was in the 1.4 million range so far in 2012.

The National Constitution Center, a block north of the visitor center, has also seen an uptick in visits. The NCC, which has been showcasing "From Asbury Park to the Promised Land: The Life and Music of Bruce Springsteen" (through Sept. 3), attracted 186,509 visitors in May and June, officials there said. That compares with 180,281 visitors during the same two months last year.

Hotel occupancy rates in Center City were up for June, as summer tourism and strong convention business kicked in, to 85.3 percent, a 4 percent increase over June 2011, according to preliminary figures compiled by Smith Travel Research and supplied by the Greater Philadelphia Tourism and Marketing Corp.

Average room prices increased by 11 percent to $185.78, the Smith figures show.

At the Barnes Foundation, whose opening on the Benjamin Franklin Parkway in May attracted national and international attention, attendance has been nothing short of sold out, officials said.

"We're very happy," said Gillman. "Absolutely, we're fulfilling our expectations."

When the gallery first opened in mid-May, a series of computer problems led to lines and some grumbling among visitors compelled to wait for access to the galleries. The Barnes admits a maximum of about 150 an hour to view its collection.

Gillman said the computer and ticketing problems have been resolved.

"Our issue has been once you open, not to disappoint people," he said. "Demand is huge."

Across the Parkway at the Franklin Institute, demand has been very strong for the "Dead Sea Scrolls" - an exhibition encompassing 20 of the ancient scrolls and hundreds of related artifacts from Israel - which opened May 12 for a run through Oct. 14.

"Our summer is up about 10 percent over last summer," said Troy Collins, Franklin Institute senior vice president for marketing, projects, and business development. "The 'Dead Sea Scrolls' is absolutely instrumental in driving that."

Collins did not have exact figures, but he said that "since Memorial Day there have been well over 150,000 visitors."

Demand to see the scrolls exhibition has been so strong, he said, that the museum has decided to remain open until 7 p.m. every night through the end of summer. (Usual closing time is 5 p.m.)

"That [demand] is something we haven't seen before," he said. In the first week of August, Collins said, the 10 scrolls currently on display will be replaced with another 10 (to preserve the fragile artifacts). In addition to protecting the scrolls, swapping could well bring visitors back, he said.

Gail M. Harrity, president and chief operating officer of the Art Museum, said about 250,000 people attended "Van Gogh Up Close," which ran from Feb. 1 to May 6. Those visitors came from every state and from 62 foreign countries, she added.

The current special exhibition, "Gauguin, Cézanne, Matisse: Visions of Arcadia," which opened June 20 and closes Sept. 3, is expected to draw 100,000 during the summer, she said.

The Rodin Museum, completely refurbished over the last three years and closed from September 2011 until July 13, has seen "very strong" visitor interest since reopening, Harrity said. Over its first weekend, the small museum next to the Barnes gallery on the Parkway drew 3,300 visitors.

"It's a very strong start," said Harrity. "With the combination of "Van Gogh," Rodin, and "Arcadia," we've been on a very strong roll."

Convention business has also been strong this summer, said Jack Ferguson, president and chief executive of the Pennsylvania Convention and Visitors Bureau.

June has seen two large conventions. The American Diabetes Association Scientific Assembly brought about 11,000 to town, the largest gathering here of the year so far. The Drug Information Association brought in about 8,000 attendees.

The diabetes convention had an economic impact of $55 million, Ferguson said. The drug information gathering put about $27 million into the local economy, he said.

"Summer was lighter last year," he said. "[2011] was better than '10 and '12 is better than '11. We're going in the right direction."

Ferguson said that hotel usage, counted in room nights, was up 66 percent through May of this year, compared with the similar period last year.

Contact culture writer Stephan Salisbury at 215-854-5594, ssalisbury@phillynews.com, or follow on Twitter @SPSalisbury.