The concept of time travel is hardly a novel one on TV.

“7 Days,” which has its two-hour premiere at 8 tonight on UPN, offers a slightly different wrinkle on the idea, giving it an “X-Files” twist.

An elite, covert military intelligence unit (is there any other kind?) seeks to design a high-tech spherical device, code named Back-Step, that allows one human to go back seven days in time.

The device isn’t operational, but the timetable gets accelerated when Chechnyan terrorists kill the U.S. president, vice president and the Russian president in a suicide bombing.

The group enlists former CIA operative Frank Parker, then ensconced in a mental hospital after an operation gone awry in Somalia. Blessed with a near-photographic memory and a high pain threshold, Parker, played by Jonathan LaPaglia (“New York Undercover”), is chosen as the best candidate for a mission that has little chance of succeeding.

He is supported by a staff that includes his old military buddy Donovan (played by Don Franklin of “seaQuest DSV”), science chief Dr. Isaac Mentnor (Norman Lloyd of “St. Elsewhere”), and scientist and obligatory love interest Olga Vukavitch (Justina Vail).

The bloodied Parker survives the journey and meets all these people again, none of whom now know him. They race to use the information he has brought back to try to thwart the assassination attempt.

After “7 Days” gets past a rather dubious explanation of how time travel works (of course, it involves aliens and Roswell), the show picks up the pace and turns into suspenseful action.

The series is most likely to be compared with “Quantum Leap,” but it lacks the warmth and characterization which the NBC show possessed in abundance. Still, “7 Days” is a pleasant change of pace from the sitcoms and angst-fests also airing at 8 p.m. Wednesdays.

Also tonight, the sniggering began as soon as the concept for the new drama “Charmed” was announced.

Schlockmeister Aaron Spelling hired Shannen Doherty, the former enfant terrible of his “Beverly Hills 90210,” to play a witch. “Type-casting” was the general theme of the comments.

But Doherty proves effective as driven Prue, the oldest of the Halliwell sisters. She teams with Holly Marie Combs (“Picket Fences”), who plays refereeing middle sister Piper, and Alyssa Milano (“Melrose Place”), a late addition to the cast as flighty younger sister Phoebe.

In tonight’s premiere at 9 on WB, the three sisters have just moved back into the grand San Francisco Victorian home of their childhood. Directed by a message on a Ouija board, they find an ancient tome and discover that they are the prophecied “Charmed Ones,” good witches who must battle growing forces of evil.

Prue has the power of telekinesis, the ability to move an object with her mind. Piper has the ability to freeze time. Phoebe is precognitive, able to see glimpses of the future.

“Charmed,” created by Constance M. Burge (the too-brief soap “Savannah”) isn’t a comedy like “Bewitched” or “Sabrina.” Instead, it’s about the three sisters’ attempts to keep their new powers a secret and cope with the unexpected challenges destined to come their way.

“Charmed” should quickly cast a spell over fans of “Buffy the Vampire Slayer,” although it isn’t nearly as sharply written as that WB hit. Whether it can break out of the genre ghetto and survive will depend on how well the three sisters and their missions are developed.