One of the most sharp-eyed and politically attuned filmmakers of her generation, Kelly Reichardt blends her lucid observational approach with a topical-thriller format to engrossing effect in "Night Moves." Perfectly consistent with the director's earlier films in its political dimensions and fascination with nature as both backdrop and subject, this tale of three environmental activists planning a dangerous act of eco-terrorism has a quietly gripping first hour that builds to a suspenseful peak, then yields faintly diminishing returns thereafter as the doubts and implications set in. But if Reichardt doesn't quite stick the landing, she's nonetheless made her most accessible, plot-driven picture to date, albeit one that may still seem too glacial by mass-audience standards to see more than a modest arthouse turnout.

Reichardt has expanded her scope and stretched her talents with every feature since rising to indie prominence with the microbudget two-hander "Old Joy" (2006), and it's been fascinating to see her retain her personal-cinema principles while adapting to the challenges of a more expansive (and expensive) canvas each time out. With its genre elements and name leads (Jesse Eisenberg, Dakota Fanning and Peter Sarsgaard), "Night Moves" is unlikely to draw the same critical attention as the more rarefied "Wendy and Lucy" and "Meek's Cutoff"; it's neither the commercial sellout that purists may have feared nor the sort of revelatory breakthrough that would spell major crossover potential. (The modest B.O. performance of Fox Searchlight's far flashier eco-terrorist thriller "The East" may provide a useful point of comparison.)

"Night Moves" is, instead, precisely the sort of intelligent, measured thriller Reichardt's admirers would expect from her brand of patient realist filmmaking, a picture that starts slow but quietly gets its hooks into the attentive viewer. Writing with her usual scenarist, Jon Raymond, the director makes effective early use of establishing shots, silences and scraps of conversation to establish the secret plans of Josh (Eisenberg) and Dena (Fanning), two Oregon-based environmentalists who have been radicalized to the point that working on agricultural communes and raising awareness at documentary screenings are no longer enough.

And so they purchase a small boat (whose name gives the film its title), acquire fake IDs and meet up with Harmon (Sarsgaard), an older ex-Marine who knows a thing or two about explosives. Together they plan to blow up a nearby hydroelectric dam and send a message to those who think it's OK, as Josh puts it, to "kill salmon just so you can run your fucking iPod every second of your life." But Reichardt, whose past several films were subtle expressions of liberal despair, proves just as willing to confront the delusions of the extreme left, and her focus here is the point at which vaguely stated ideals become irrevocable realities.

Thus, apart from a few doom-laden statistics about the sorry state of marine biodiversity, the characters here don't spend too much time mouthing off about their political agendas, as they're already on the same page anyway. Instead, the film focuses on procedural details, all the tiny ways in which the best-laid plans can go awry; acquiring 500 pounds of ammonium nitrate fertilizer without arousing suspicion, for instance, turns out to be a trickier proposition than they expected. The result is an intimate, coolly insinuating portrait of conspiracy in action, and viewers may be surprised at how tense they find themselves -- and how invested they have become question of at what point -- and at what cost -- as Josh, Dena and Harmon prepare to execute their mission.

"Night Moves" might have been close to perfect had it clocked in at a tight 80 minutes or so, rather than pushing on for another half-hour. While the fallout is impressively handled in its own way, the suspense and momentum inevitably dissipate as the story slowly moves toward a credulity-straining climax. Still, a feeling of deflation is entirely in keeping with the note Reichardt means to end on, and she finds just the right closing shot with which to convey exactly what her characters have and haven't accomplished.

The three leads manage the tricky task of drawing the audience into complicity but not sympathy with their characters, all cold, cynical types who are often curt and withholding in their dealings with one another and the outside world. (The press materials reveal more backstory than the film does.) Eisenberg gets the dominant perspective, and while he's entirely believable as the most contemptuous and also most committed of the trio, the decision to make Josh so taciturn, robbing him of the actor's trademark verbal agility, reduces the character to a series of increasingly paranoid and paralyzed reaction shots in the final reels.

Production values are spare but crisp and exacting. Reichardt, always attuned to environment in the most basic storytelling sense, delivers her own moving tribute to Mother Nature with a poignant, wordless sequence in which Josh, Dena and Harmon row their boat past a wooded area conspicuously devoid of trees, Christopher Blauvelt's crystalline HD images merging to mournful effect with composer Jeff Grace's moody chordal progressions.
