Brent D. Glass, director of the National Museum of American History for the past nine years, announced Monday that he is retiring in July.

Glass, 64, led the museum through a two-year renovation, creating an open public space with a new display of the Star-Spangled Banner. The museum, the third-most popular of the Smithsonian complex, was closed during that time.

In a phone interview, Glass said his decision to retire was prompted by a desire to promote history education. “I have a lot of different ideas on how I want to be most effective in promoting history education and public memory,” said Glass, who will remain a senior adviser at the Smithsonian until the end of the year.

Glass didn’t give specifics about a future job but said he had been brainstorming. “David McCullough is a very good friend, and he has been so active about taking history education to the forefront. There are people like Sandra Day O’Connor and Richard Dreyfuss, who among others, are talking about the lack of knowledge about history,” he said.

Before coming to the Smithsonian in 2002, Glass was executive director of the Pennsylvania Historical and Museum Commission.

In addition to the $85 million renovation of the building, Glass lists other accomplishments, such as the transportation hall that opened in November 2003 and an expansion and more visibility for the Lemelson Center for the Study of Invention and Innovation.

The American History museum has about 3 million artifacts and is constantly adding to its archives. Among the most famous are Dorothy’s ruby slippers from “The Wizard of Oz” movie; Julia Child’s kitchen; a Woolworth’s lunch counter that was the site of the first student sit-in protest; and the port­able desk on which Thomas Jefferson wrote the Declaration of Independence.

Glass said one of the important donations during his tenure was firefighting memorabilia from the 19th century given by the Cigna company. But he said pop culture gifts were significant, too. Included would be Jerry Seinfeld’s puffy shirt from the television show “Seinfeld” and a gown from the Grammy Awards that Nancy Wilson donated recently.

“You can’t have more fun than being director of the American History museum. You have so much variety. You get to solve problems of consequence. And I like to say we are in the forever business.”