By the laws of television physics, “Ghost Whisperer” never should have worked for CBS.

It’s a supernatural fantasy drama on a network known for its true-grit forensic procedurals. It revolves entirely around a young female lead, Jennifer Love Hewitt, in contrast to the rest of the Eye’s roster of rugged male stars. And from the start, the show was scheduled in a low-visibility Friday night timeslot.

But as “Whisperer” nears the end of its fourth season, the show continues to defy gravity. Total viewership is up 28% from last season, to an average of 11 million viewers per week, and the show has won its 8 p.m. hour every week this season. More impressively, the skein has hit series highs this season in the most elusive demos for CBS, adults 18-34 (up 20%), women 18-34 (up 26%) and women 18-49 (up 27%).

And it will likely enjoy another bounce next season when repeats of “Whisperer” begin running on Sci Fi Channel.

So what gives? How did this show about a woman who communicates with the dead succeed in busting so many conventions? A lot of it can be chalked up to the iron will and marketing savvy of its stewards, exec producers Ian Sander and Kim Moses.

As TV vets, Sander and Moses, who are married, were well aware of the high hurdles “Whisperer,” a co-production of ABC Studios and CBS Paramount Network TV, faced when it bowed in the fall of 2005.

“We just knew we needed to get a drumbeat going before the show hit the air,” Moses says.

Sander is candid about the sense of urgency they felt, given the timeslot and other obstacles they faced. After years of producing telepics and such series as “I’ll Fly Away” and “Profiler,” Sander and Moses had produced a number of pilots that didn’t go the distance. They knew that TV had gotten only tougher in the decade since “Profiler” bowed on NBC.

“We just took everything we’ve learned in our time in the business and brought it to bear on this show,” Sander says.

In the years before they developed “Whisperer” with series creator John Gray, Sander and Moses did a lot of work on original Internet productions and digital marketing campaigns, as producers and as consultants.

They knew “Whisperer” had built-in Internet appeal through its subject matter and its Web-friendly star. They seeded the Web with videoclips and other material tied to the show and to Hewitt in the months before its premiere. On the ground, Sander and Moses worked the phones to organize grassroots tune-in efforts and promotions on college campuses, where Hewitt is well known to contempo co-eds from her turns in the “I Know What You Did Last Summer” horror pics and Fox’s 1990s ensembler “Party of Five.” The show got another jolt of Gen-X appeal with the addition this season of Jamie Kennedy (and in recent weeks the gossips have been abuzz with the budding romance between Kennedy and Hewitt).

“Whisperer” is a cross between a lighter version of “Buffy the Vampire Slayer” and an edgier take on “Touched By an Angel.” It also has classic CBS gumshoe procedural elements, except that “Whisperer’s” plots involves helping the dead settle their last Earthly scores and “cross over” to the Light Side — or in some unfortunate instances, the Dark Side. Even with its growth spurt this season, “Whisperer” doesn’t have a whole lot of cachet in the creative community. But what it lacks in showbiz buzz it makes up for in fandemonium among nonpros.

With its themes of the afterlife and extrasensory perception, “Whisperer” was tailor-made for building a strong following among true believers. Its bona fides in this realm are strengthened by its association with self-styled “spirit communicators” James Van Praagh (who is a co-exec producer) and Mary Ann Winkowski, the inspiration for Hewitt’s Melinda Gordon character.

Sander and Moses began plotting multiple viral Web campaigns to promote the show back when network execs’ idea of digital marketing was putting a “Whisperer” page on the CBS.com website.

Sander and Moses had no budget for their extracurricular marketing activities, so they found a way to do them inexpensively, and on the fly. And in the four years since, Sander and Moses still work around the clock on the care and feeding of the show. The two supervise all day-to-day aspects of production and frequently direct segs, but the writing team is overseen by exec producer P.K. Simonds.

Once “Whisperer” proved it had staying power, Sander and Moses went into overdrive to expand the show’s brand as far and wide as possible. That meant everything from sales of clothing and other items seen on the show — when she’s not chasing after ghosts, Hewitt’s character runs a curio shop — to trading cards, comicbooks (through publisher IDW), novelizations (through Pocket Star Books) and a coffee table “Spirit Guide” book published in November through Titan Books.

A big breakthrough came in the second season when Sander and Moses sold General Motors on the sponsorship of a series of webisodes, “The Other Side” — which are now in their third cycle. GM hadn’t been a sponsor of the TV series until it partnered with them on the webisodes, which cleverly showcase various GM models amid the spooky four-minute installments.

For all the ancillary business Sander and Moses have developed, the Web remains the engine behind their marketing initiatives. Through clues dropped during the TV episodes, the webisodes and the tarot card deck included in the DVD box set of season three, fans have been sent to search out websites and faux blogs — including andshamethedevil.net, rubloodymary.com and penthius.info (a handy site for researching ghosts) — that in one way or another fuel the “Whisperer” mythos.

And then there are the independent fan sites that “Whisperer” happily plies with all manner of material and behind-the-scenes vid tidbits. (Full episodes of the show itself are not available for paid downloads or web streaming, due to deal issues between ABC Studios and CBS Par.)

Last summer, with little support from CBS or its production studios, “Whisperer” pitched its tent at ComiCon and caused a traffic jam on the confab floor as geeks lined up to get a peek at Hewitt.

The totality of the Sander and Moses vision for exploiting, in the best sense of the word, the show’s marketing potential has earned the admiration of the network and their studios. The pair were recently asked to give some of the other showrunners at ABC Studios a tutorial on how they harnessed the power of relatively inexpensive digital media tools to tubthump their baby.

“We couldn’t have done what we’ve done 10 years ago,” Moses says. “But the evolution of technology on every platform has made it accessible for us. We’re like a mom and pop shop.”

As much as “Whisperer” has proven itself a 21st century hit, Sander sees the challenge that producers and nets face in drawing attention to shows in a bazillion-channel universe as something of a throwback to an earlier Hollywood era.

“It used to be that the job of being a producer meant doing everything. Then people started to be specialists,” he says. “This is a good time to be an old-fashioned Hollywood storyteller. It’s a good time to know how to produce something for $1,000 or $100,000.”