Although it feels longer than the push to Baghdad and tells you more than you may want to know about weapons of mass destruction, the four-part documentary "Avoiding Armageddon," which debuts tonight at 9 on PBS, is a generally clear-eyed look at the post-9/11 world and a useful guide to what should really concern us about terrorism.

More important, it's a guide to what not to worry about, and a helpful antidote to the sky-is-falling hysteria that has recently been filling newspapers with calls for duct tape, gas masks and inflatable kayaks in the basement.

Nevertheless, after viewing the chilling images tonight of infected smallpox victims, you may want to get your vaccination.

Tonight's two-hour segment -- "Silent Killers" -- deals with biological threats; tomorrow's is "Nuclear Nightmares." The last two chapters deal with the roots of terrorism in the economic and spiritual chaos of the Third World, and with turning the tide against both the conditions that breed terrorists and the specific weapons they wield.

Ultimately, the series stresses that no action or actions by any government can totally eliminate the threat of terrorism in our current world climate and we had best come to grips with that reality.

Likewise, given the randomness of terrorist threats, it says the only meaningful short-term precautionary steps are collective -- particularly at the neighborhood level -- such as the measures that groups in Tokyo and San Francisco have taken to provide quick rescues in the face of recurrent natural disasters like earthquakes.

"Avoiding Armageddon" is the inaugural production from Ted Turner Documentaries and perhaps inevitably spends most of its time telling us how we got where we are in the WMD and terrorism business.

The most intriguing aspect of tonight's program is the recollections of Yoshio Shinozuka, who as a young Japanese soldier was assigned to Unit 731, a germ warfare horror shop used to wipe out something like 200,000 Chinese during World War II.

Unit 731 has been amply documented -- tonight's program includes archival film. But it has rarely been treated by historians though its workings were every bit as ghastly as anything dreamed up by the Nazis. Moreover, though Shinozuka has spent most of his life trying to ease his conscience for dissecting live subjects and spreading plagues in Asia, the Japanese government has never acknowledged that Unit 731 existed. And the U.S. government, in one of its darker, less enlightened moments, permitted Japan's germ-dealing war criminals to escape postwar prosecution in exchange for the Faustian discoveries of the Unit 731 scientists.

Tomorrow night's program points out that nuclear terrorism is an eminently avoidable threat, since even the most malevolent terrorism can't come up with the vast infrastructure needed to produce weapons components such as plutonium. The danger, the program shows, is that much of the world's supply of bomb-ready plutonium already produced is housed in the near equivalent of backyard garages in Russia under a security system vulnerable to any terrorist with a serious bolt-cutter. Securing it or eliminating it is only a matter of money, making nuclear terrorism the most preventable WMD threat there is.

These and other stories are provocative stuff, as are interviews with Saddam Hussein's onetime atomic bomb builder and a 17-year-old Palestinian pondering a future as a human bomb.

"Avoiding Armageddon" is not exactly comforting viewing. But to its great credit it plays to the mind, not the emotions, and posits some instructive steps to steer us away from doomsday. Most of all, it treats its audience like adults and suggests we act like adults in acknowledging that we've been living in a dream world too long. We're now face to face with the apocalyptic terrorism much of the world lives with every day.

We'd do well to acknowledge that fact soberly, the series suggests, and then, like the rest of the world, get on with our lives.

The PBS series is a valuable guide on what not to worry about.Israeli nurses receive smallpox vaccines in a scene from Ted Turner Docu-

mentaries' "Avoiding Armageddon," a four-part series that begins tonight.