When Joseph M. Torsella returned to the National Constitution Center in 2006 for a second term as chief executive, he was called a "transitional" leader to tide the center over for a few years.

"Initially, I thought it was going to be very brief," Torsella said yesterday after the center announced he was stepping down next month to pursue other, still undetermined, interests.

The center will name an interim chief before Torsella departs in January, and Torsella said he would help conduct a search for a long-term leader.

"I don't think the next CEO should be a two-year person. It should be someone who's here for eight to 10 years, who wants to grow into maturity with the institution," he said.

Torsella, 45, who got the institution built at 525 Arch St. during his first stint, said he broadened the center's profile during his second wind.

The center hosted several events during the presidential election that thrust the institution into the national spotlight, including the final debate between Hillary Rodham Clinton and Barack Obama. Torsella also persuaded former Presidents George H.W. Bush and Bill Clinton to serve as chairmen of the center's board.

"It's not a tender, vulnerable institution any more, and I think the year 2008 has really shown that," he said.

Torsella led the center's organization from 1997 through the opening of the building in 2003. He was replaced by Richard Stengel, who resigned in 2006 to return to Time magazine as managing editor.

After Torsella left the center, he mounted an unsuccessful campaign in 2004 for the Democratic nomination in the 13th Congressional District. He also worked as a consultant and served as the unpaid chairman of the group that made a bid for Philadelphia to host the 2016 Olympics.

"Joe Torsella has served our center with great honor and distinction," Bush, the outgoing chairman, said yesterday in a statement. "It's understandable that someone with his talent would seek other challenges, but the center will miss him."

Torsella, a Rhodes scholar who was a deputy mayor before assuming the Constitution Center role, said he was uncertain what he would do next, but it might be something political - a pursuit he said he could not comfortably undertake as head of the nonpartisan, nonprofit Constitution Center.

"I want to look at all the possibilities and options, and I want to do it in kind of a clear-headed way away from what is properly a demanding and bipartisan job here," he said. "I'm looking forward to clearing my mental decks and figuring that out."

Torsella, whom Gov. Rendell named in August to head Pennsylvania's State Board of Education, said that whatever he did, he did not want to move from the area.

"I'm rooted here: kids, commitments, house, family, love, passion. This is my home."