NEW YORK — At Showtime, the bosses are accustomed to having a very narrow window of opportunity.Like competitor and fellow premium service HBO, Showtime needs edgy, critically acclaimed series to convince customers they’re getting more than they would from a broadcaster or basic cable. But they can’t be so odd as to eliminate the chance that a large number of people would like them.

So with “Weeds” you get a story about a typical suburban family — whose mom happens to deal drugs. And on “Dexter” you get an investigator who is expert at studying blood stains to solve crimes, yet also happens to be a serial killer.

“It can’t just be the greatest forensic cop show,” Showtime programming chief Bob Greenblatt said. “It has to be a forensic cop show with a twist, because that twist is going to be what gets us noticed among all the other shows that are out there.”

Despite the limitations, Showtime is closer than it has ever been to establishing its own brand for original product. “Weeds” may be a signature series after showing strong growth in its second season this fall. “Brotherhood” drew such laudatory reviews that sister station CBS aired an episode, and the still-growing series “The L Word” is back in January.

Showtime received 19 Emmy nominations this year, the most in its 30-year history.

The most important thing for Showtime is an original series so compelling that people feel they must subscribe, said Larry Gerbrandt, general manager of Nielsen Analytics and a cable-industry expert.

“I think `Weeds’ was a surprise hit for them,” he said. “It’s not that they haven’t been trying. They just haven’t had anything like ‘Sex and the City,’ `Six Feet Under’ or ‘The Sopranos.’ That’s what they’re striving for.”

Ah, yes. HBO.

No article about Showtime would be complete without mentioning it. HBO has twice the number of subscribers as Showtime, which has about 14 million. HBO also has twice the money to spend on programming, probably more, Gerbrandt said. Still, that is the extremely high standard Showtime is held to.

But with “The Sopranos” due to start its final season and HBO unable to replace “Sex and the City” with anything nearly as popular, Showtime has a special opportunity to look good in comparison.

“I’ve been asked that question for 20 years, and it’s much easier to answer that now,” said Matthew Blank, Showtime chief executive, about how his network distinguishes itself from HBO. “We’ve got a lot of momentum behind the choices we have made over the last couple of years at Showtime, and that’s really important to us.”

Only six months ago, Blank had to deal with a damaging public rebuke from his boss, CBS Corp. chief Leslie Moonves. Moonves said in June that Showtime seemed “a little bit too much of an off-Broadway play” and needed to go more commercial.

“It was giving them a friendly nudge,” Moonves said this week. In fairness, he believed Blank and Greenblatt were already headed in that direction. Moonves said he’s happy with the way “Weeds” and “Dexter” did this fall, believing those shows were an example of what he was talking about.

The initial comment exasperated Blank, who said Moonves was referring to an older Showtime and series like “Queer as Folk,” not the current network.

“We didn’t want to ever go completely mainstream because that’s what network television does,” Greenblatt said. “But there have been some shows in the past that were particularly narrow, whether they were ethnically narrow or conceptually narrow. I think we’re consciously trying to widen the berth a little bit.”

The attention given to stars like Mary-Louise Parker of “Weeds,” who won a Golden Globe Award in January as television’s best comic actress (and was nominated again Thursday), and former “Six Feet Under” mortician Michael C. Hall in “Dexter” (also Globe nominated) has made well-known actors more interested in Showtime projects, Greenblatt said.

That, along with Showtime’s broader focus, is reflected in three series the network is developing.

“Sex and the City” creator Darren Star, who just got done with a series about four female best friends in New York, is behind “Manchild,” a remake of a British series about four male best friends in Los Angeles. One of Carrie Bradshaw’s old boyfriends, John Corbett, is in the “Manchild” cast.

Andie McDowell and Lara Flynn Boyle are in the cast of “Insatiable,” a story about four families in rural Illinois where everyone has an addiction. In another prospective series, David Duchovny plays a sex addict who is also a divorced dad of a teenaged girl.

Successful series are also crucial for Showtime because, as Blank explained, the idea of movies as the chief draw is over. Between theaters, DVDs and on-demand services, people have many options to see movies before they reach premium cable. Compiling series on DVD sets or selling them in syndication represent huge new revenue sources (the A&E Network paid $195 million for “The Sopranos,” which is about to begin its run on basic cable).

These are revenue sources the network has some control over, important because there doesn’t seem much traditional growth in premium cable, Gerbrandt said. Showtime’s subscriber level hasn’t substantively changed over the past two decades.

To a large degree, Showtime’s subscriber base is dependent on factors beyond the network’s control, like whether cable or satellite systems offer it as part of a package, he said. And premium cable is often the first thing to go when people are looking to save money.