Rome, not having been built in a day, certainly doesn't fall in one, either. In fact, after 12 hours and five nights of the NBC mini-series "A.D.," Rome still hasn't fallen, only wobbled a little. So will viewers who make it all the way through this handsome but painfully poky and talkative saga set in roughly the first 64 years after the crucifixion that founded a religion.

"A.D." opens and closes with three-hour chapters Sunday and Thursday at 8 on Channel 4. The three chapters in between are two hours each and air at 9 p.m. Monday, Tuesday and Wednesday. "The past blurs," James Mason as Tiberius notes; this mini-series is so long, the present blurs as well. Not for nothing did West Coast wags dub it "O.D." at press screenings earlier this year.

Timing is everything in the world of modern broadcasting empires, and NBC hopes sufficient millions of viewers will be in tolerantly reverential Holy Week moods so as to sit through all the ham and yammer of "A.D." Once more into the arena -- where, in Part 5 of "A.D.," the Christians go up against leopards and tigers and dogs (oh, my!). And once more the pageantry of biblical movie cliche's, like the Roman soldier who converts to the faith, and those wicked wicked dinners at Caesar's palace. We haven't just seen it all before; we have seen it all a hundred times before.

Where a ray of intelligence peeps through is in the script by Anthony Burgess and Vincenzo Labella, who have tried to keep the film historically and scripturally accurate even while inventing fictional proletarians whose lives are played out against this moment of seismic change. Real people depicted behave more or less according to what scholars have written, and there seems an honest attempt to recreate everyday life in 1st-century Rome, not just stage "Dynasty" as a toga party, and to deal on a fairly serious level with matters like religious persecution, sectarian territorialism and the perennially uneasy relationships between church and state.

They also make a brave effort at analyzing the very elements of mortal faith, perhaps never summarized more succinctly than in words of Jesus quoted in the film: "Blessed are they who have not seen, and yet believe."

There's even some decent imagery. The very opening shot, a close-up of the sign above Christ's head being yanked off the now empty cross, makes a strong first impression. And later, the sight of Caligula stabbing at the reflection of the moon in a palace pool makes a piquant one.

Then suddenly the thing will lapse into banality, as during an exchange among the disciples in part one: "You doubt our word, man?" "Thomas is the name. Thomas." Much later, Caligula's crimes are listed, with a straight face, as "rape, mutilation, and confiscation of property." Yes, it was probably confiscation of property that did him in. He is knifed several times on his way to the men's room at the Colosseum during a seventh-inning stretch.

"A.D." is hardly a kitsch stitch along the lines of last year's risible "Last Days of Pompeii." It's on a much more earnest level; and that may be in part its undoing. The film is rated not PG but P&G; it is a Procter & Gamble production. Therefore, there is much less of the violence and sex one usually finds in these epics. And, seemingly, much more talk. The gladiator scenes are all rather tame, and Caligula's and Nero's wickedness tidied up and overdressed.

Any film set in this ripe epoch and running to such exasperating length is bound to harbor a certain amount of Truly Dreadful Acting, and with a huge cast, director Stuart Cooper could hardly have elicited unanimously good performances. Besides, he was keeping the momentum under control -- mainly by making sure there was barely any.

Of the four Caesars portrayed, Mason, in his last film role, is touching as creaky Tiberius, who pouts on the isle of Capri and smacks a cheeky intruder's face with a fat fish. John McEnery makes a suitably hysterical Caligula. Richard Kiley is utterly awful as the stammering Claudius. And Anthony Andrews, once Sebastian in "Brideshead Revisited," gets to chew scenery, props and about six of the seven hills of Rome as Nero, the idiot pervert.

Then there are the invented ordinary people who try to cope with each new version of Hellzapoppin' to play the palace. Some are Jews, some are Nazarenes (Christians, as they come to be called in the seventh or eighth hour or so), some are servants of the state, many are its victims. There are so many it is hard to keep track, but Cecil Humphreys is a virile asset as Caleb and Diane Venora an appealing, no-nonsense Corinna. Unfortunately, we are asked to believe that Corinna is a female gladiator, an unlikelihood obviously concocted more as a sop to contemporary sensibilities than as a reflection of how things were 1,900 very odd years ago.

If you're looking for Ava Gardner, you have a long wait. She does appear, but not until well into chapter four, in the role of Agrippina, mother of Nero. The writers give no indication of whether she was a monster or a cipher, and neither does Gardner, though she leans toward the latter. Jennifer O'Neill is seen effectively but briefly as Claudius' wife. Ben Vereen happens along in Part 3 in a role so expendable you figure he's there mainly as a kind of mini-series good-luck charm. NBC's boast of an "all-star cast" rings hollow.

One unseen star in all this is Albert J. Whitlock, the celebrated visual effects artist who flew Hitchcock's birds for him and has made many another artful movie lie look legit. For "A.D." he rebuilt Rome with ingenious camera and processing tricks, and burned it strikingly for the finale. The film, photographed in Tunisia and Italy by Ennio Guarnieri, is as visually impressive as was "Jesus of Nazareth," an earlier mini-series from some of the same creative team. It is hard to think of fictional TV films more beautiful to behold than these. Again, though, 12 hours is a heap o' beholdin'.

Aspiring filmmakers can use inflated time killers like "A.D." for editing practice. They can sit in their homes and edit out all the scenes that are unnecessary or repetitious. By the time the mini-series is over, you'd have enough of those to make an entire feature-length film. The theological colloquies and the Senate debates do go on. You don't have to take my word that it's a long, hard crawl, of course. But lucky are they who have not seen and yet believe.