Charles Blitzer, assistant secretary of the Smithsonian for history and art, will become the new director of the National Humanities Center in North Carolina.

Blitzer, 55, will assume his new post early next year. He replaces William J. Bennett, who left the center in Research Triangle Park, N.C., last January after President Reagan appointed him chairman of the National Endowment for the Humanities.

"I have terribly mixed feelings about all this," Blitzer said yesterday. "I have wonderful friends here and I like Washington and I like working with the people at the Smithsonian, but when you find the ivy growing up your leg, it's time to move."

Blitzer, who holds an undergraduate degree from Williams College and a PhD in the history of political theory from Harvard University, came to the Smithsonian in 1965 as director of education and training. He became assistant secretary for history and art in 1968.

The National Humanities Center is nonprofit and privately funded. It annually houses about 40 fellows -- "some academics and men and women of affairs," Blitzer said -- for study in the humanities. Blitzer becomes the third director of the 5-year-old center.

"It sounds like an exciting place," said Blitzer of the center whose board is chaired by Edward Levi, a former U.S. attorney general. Blitzer added, "The most persuasive argument used by the board is that the center is well-funded for the next few years and is going well, but it's still new enough so that a director who does have ideas -- which I hope I will -- can still shape it."

The board first approached Blitzer last winter when it wrote him to say his name had come up for consideration. "I wrote back and said that I was very flattered but very happy here. But then time passed and I was persuaded that it was the place to go to . . . It has an extraordinarily impressive board of directors and an interesting collection of fellows from all over the place."

"He was the best candidate," said Kent Mullikin, assistant director of the center. Mullikin said the search committee was looking for someone "with solid administrative experience and someone also at home in the scholarly world. Anyone you talk to will tell you he's just tremendously admired and very capable."

"I'm sure they were looking for someone who would be a respected scholar, a figure of some prominence and a fund-raiser," said John Agresto, formerly of the National Humanities Center and now assistant chairman of the National Endowment for the Humanities.

Asked if he would be doing fund raising, Blitzer said, "I would be surprised if I didn't."