The Cold War audience faced the constant threat of nuclear annihilation, a risk seen in everything from fanciful spy yarns to “Failsafe” to “Twilight Zone” episodes. With rare exceptions Doomsday was averted, often with “007” to spare.

In the post-Sept. 11 age, however, disaster scenarios have graduated from the Bondian world of power-mad villains to a more reality-based level of fear. It’s against this backdrop — as the public puzzles over how to process color-coded “terror alerts” — that networks have begun redrawing the boundaries of what constitutes entertainment.

Next month marks a bit of a watershed in this regard, with the U.S. premiere of two U.K. imports that ratchet up the fear factor. The first up “Smallpox,” FX’s documentary-style look at a smallpox epidemic, followed by HBO’s “Dirty War,” about a devastating “dirty bomb” attack in London. Both are from director Daniel Percival, who is not a guy to sit next to at a party if you specialize in long-term retirement accounts.

“It’s all true,” say the promos for “Smallpox,” in which a terrorist triggers a devastating outbreak. “It just hasn’t happened yet.”

Along with those two little rays of sunshine, Fox’s “24” returns for another very bad day, after last season’s biological attack that killed hundreds in a Los Angeles hotel. Not surprisingly, the network’s promos are loaded with testosterone: “As the world grows more dangerous, so does he. Jack’s back!” they say of the show’s unlucky hero, played by Kiefer Sutherland.

These productions offer a more unflinching view of the terror threat than that displayed within broadcast news. Indeed, despite fear-based appeals about food poisoning in restaurants, shark attacks and paroled pedophiles, newscasts still tend to close on a soothing note, usually with a story about a panda that’s adopted a kitten, or something equally weighty.

Not so with “Dirty War” and “Smallpox,” which present acts of mass murder that would produce widespread hysteria. Ditto for “24,” which has frequently found its story lines uncomfortably mirroring current events.

Drama paralleling reality is always a possibility, of course, as was the case with “The China Syndrome,” whose 1978 release was followed less than two weeks later by the Three Mile Island nuclear accident. Yet these dramatizations strike so close to home with such blunt force it’s hard to discern what the audience reaction will be, in part because entertainment and news remain so conflicted by this issue.

Remember, just a little over three years ago some feared “24” wouldn’t survive the fallout from Sept. 11, along with two other spy-themed dramas premiering that fall: ABC’s “Alias,” which also returns in January; and CBS’ since-defunct “The Agency,” whose pilot contained a reference to Osama bin Laden.

Clearly, viewers could distinguish between fact and fiction, but “Smallpox” and “Dirty War” provide an even grittier foray into the world of what-might-be — and what some experts say inevitably will be — in a far more alarming manner. By that measure even U.S. news organizations, perhaps reluctant to turn off viewers, exercise greater restraint — consistently returning to less substantive threats narrowly targeted to pregnant wives or children who visit Neverland ranch.

“Obviously, there has to be a balance between truth and reassurance,” the Minister of London tells a committee in “Dirty War,” which is complemented by another character who cautions, “The more you fuel public anxiety, the more we play into their hands.”

Both observations speak to the difficult balancing act that news and entertainment divisions face — the middle ground between sticking heads in the sand or adopting the sort of feverish tone that provokes irrational hysteria. That said, it’s hard to come away from “Smallpox” or “Dirty War” with much more than a sick, helpless feeling, which, except for certain fans of reality TV, isn’t a major turn-on.

Similar questions, interestingly enough, are raised in the latest issue of CMO, a magazine aimed at marketing execs. With the exception of a spokesman at a security firm — who is surprisingly frank about the commercial benefits of fear and paranoia — most marketing gurus interviewed cited a desire to reassure anxious consumers in frightening times.

Personally, I enjoy a good scare and absorbed end of the world movies in my Cold War youth with nary a second thought. So maybe age has changed my palate, or maybe the world really does look a little different through a post-Sept. 11 haze.

Whatever the reason, bring on the vampires, werewolves and other forms of escapist mayhem, but my guess is I’m not alone in saying that dirty bombs and smallpox pustules currently aren’t my idea of a good time.