This movie isn’t the first time Denzel Washington has traveled sci-fi style through time and space in pursuit of a villain–he did the same thing in “Virtuosity” (1995). But Tony Scott’s “Deja Vu” doesn’t descend to a “Tron”-like display of computer-based images as the earlier movie did, and though in some respects it’s even more ridiculous (and in others rather unseemly), it’s not nearly as gadget-ridden, or as bad. Of course, it’s not good, either, just a middle-grade heroic action-adventure with pretensions and serious script problems.

The picture begins with a disaster in post-Katrina New Orleans: during the Mardi Gras festivities, a ferry crammed with young kids and visiting sailors is blown up in a terrorist act. Enter Doug Carlin (Washington), a hot-shot ATF agent who not only pinpoints the source of the explosion but connects it with a body of a woman, Claire Kuchever (Paula Patton), that’s washed up downstream. But further investigation shows she was killed some time before the blast, although her body was made to look as if she’d been killed in the explosion. When Carlin searches her house for clues, he discovers his own voice on her answering machine, though he doesn’t recall contacting her.

Before long Doug is tapped to join the FBI team assigned to the case, led by Jack McCready (Bruce Greenwood) and Andrew Pryzwarra (Val Kilmer). It’s not long before they introduce him to one astonishing piece of surveillance equipment, a device that downloads images drawn from satellites that show events that occurred precisely four days previously. (Unfortunately, it’s a one-time deal, requiring one should know the precise place and angle to observe; and you can’t go back and view elsewhere if you’ve picked wrong.) It allows the team, including techies Alex Denny (Adam Goldberg), Gunnars (Elden Henson) and Shanti (Erika Alexander), to spy retroactively on Claire’s life prior to the explosion–which reveals not only the identity of the bomber, but an unhappy revelation about Doug’s partner (Matt Craven).

But the mechanism, as it turns out, has a further application: it can permit Carlin to travel back in time and, perhaps, prevent Claire’s death and the ferry disaster. A tense romance is clearly in the offing, as well as lots of twists and turns involving an effort to alter the past without creating different catastrophes in the present.

Time-travel tales always have problems of logic and credibility, and this one is certainly no exception. When the team initially explains the ins and outs of their surveillance gizmo to Carlin, the technical gobbledegook flows so fast and furious that what’s comprehensible sounds ridiculous and what isn’t is positively laughable. The now-and-then nature of what follows after Doug takes the time tunnel plunge is kept relatively clear by the scripters and Scott, but that doesn’t mean that it ever really seems to fit together.

And there are some fundamental narrative bumps that make things even more fishy. One is the identity of the bomber, which not only makes for muddled motivation but, in this age of international terrorism, seems like a cop-out designed to offend only those who are used to it. Then there’s the major romantic interlude between Doug and Claire: although the duo are racing against time to get back to the site of the disaster, they stop off at her place to clean up and get to know one another before proceeding–until Washington suddenly says, “I’ve got to get going!” Duh! And then there’s the big finale, which is choreographed for maximum excitement but still cheats to provide an upbeat ending. (Resurrections are a dime a dozen in movies nowadays, and “Deja Vu” gives us scads of them, the worst at the very end. Oh, for the days of “The Parallax View,” when a picture could actually keep the courage of its convictions through to the end! In thus case, Scott even descends to the point of offering a mawkish insert involving an elderly woman awaiting her daughter on the dock. Truly shameless.)

Apart from Scott, who as usual overplays his virtuoso hand (the opening ferry sequence is staged and cut for the greatest impact, and a car chase goes positively berserk), the movie belongs to Washington, and his simmering intensity is still impressive, even if, having passed the half-century mark, he’s beginning to seem just a trifle too old for these kinds of heroics. (It’s not as embarrassing as Harrison Ford, but before long it may be.) Patton makes a solid impression as the damsel in distress he must save, and Jim Caviezel plays effectively against type, although as written his character is a simplistic caricature. Kilmer and Greenwood get through their stock parts professionally enough, and Goldberg and Henson provide the obligatory comic relief, but the script offers them all very little. Technical credits are top-notch across the board, though Paul Cameron’s cinematography is marred by the director’s hyperactive style.

There’s one final point to be made about “Deja Vu.” When “United 93” was released, some argued that it was inappropriate to use a terrorist tragedy as the springboard for what, however seriously intended, was still “entertainment.” Scott’s film is basically a genre lark, but it begins with a act that, though fictional, is equally horrifying in today’s climate–and very realistically staged. As the story veers more and more into science fiction mode, it makes that intense opening feel, in retrospect, increasingly unsettling. Maybe it’s the cheap employment of national fears for this kind of pulpish purpose, rather than a sensitive recreation like Paul Greengrass’, that’s truly problematic.