The vast permanent collection of the National Museum of American History just got a little more other-worldly with the donation of several artifacts from the television show “The X-Files.”

Chris Carter and Frank Spotnitz, creators of the sci-fi hit that ran from 1993 to 2002 and spawned two Hollywood films, were at the Smithsonian on Wednesday to watch the pilot script and other pieces of memorabilia join Dorothy’s ruby slippers and Kermit the Frog in the museum’s permanent collection.

“Standing up here feels like an X-File in itself to me,” said Carter, who wrote, directed and produced the TV series and films. “It’s an unexplained phenomenon.”

The show centered on two FBI agents who were assigned unsolved cases that involved the paranormal. It was a commercial hit and quickly developed a cult following.

Among the objects donated are the pilot script, which includes storyboards, casting lists and the producers’ notes, as well as the cross that Agent Dana Scully, played by Gillian Anderson, wore throughout the series.

The famed “I Want to Believe” poster that hung in the office of Agent Fox Mulder — played by David Duchovny — was also donated. The show ran for a total of 202 episodes and received a combined 61 Emmy, Peabody and Golden Globe Awards.

“The series is a significant representation of science fiction in television drama,” said the museum’s curator, Dwight Blocker Bowers. “‘The X-Files’ captured the genre’s penchant for the paranormal and cleverly used it to address such contemporary issues as governmental control, national and international conspiracy theories and the possibility of extraterrestrial life.”

Despite these accolades, Spotnitz, who also directed and produced the series and films, says he has had a hard time wrapping his mind around the success of “The X-Files.” After all, it is not often that a show becomes a large commercial hit with many Web sites devoted to its intricacies.

“You work on something very, very hard — this is 14 years of my life — and the influence of the show and how it reaches people is kind of interesting. It doesn’t feel real,” he said. “When the nation’s museum decides to make us a part of its collection, it makes it very real and tangible the impact the show has had.”

Carter has some familiarity with the nation’s capital. Throughout the nine-year run of “The X-Files,” he and producers often consulted with the FBI to be sure they got certain details of the job right. The relationship developed over time, and Carter was recently asked to travel to Washington, D.C., and shoot a spot for the bureau’s centennial celebration, though he says the rapport was not always so congenial.

“Right before the pilot there was a call from the FBI that said, ‘Who are you and what are you doing?’” Carter said. “I swear I thought it was J. Edgar Hoover reaching out of the grave.”

But over time the bureau grew to like the show and at one point invited Carter and its stars to come and tour FBI headquarters.

“Our relationship with the FBI became very chummy,” Carter said. “They were unofficial fans.”

Though the television show ended in 2002, a new movie featuring Agents Scully and Mulder will be released in theaters later this month. Carter says coming back to the characters “felt like riding a rusty bicycle,” but he soon found his footing and produced the script for “I Want to Believe,” which opens July 25. Despite all of these accomplishments, Carter find his success to be a bit befuddling.

“I’m just a kid from a little town in California, and now I’m being asked about the FBI and speaking at the Smithsonian,” he said. “Pinch me.”