G.I. Jane is one of those expertly constructed movies, well-paced and populated with good-looking, able performers who buzz along on the power of a solid Hollywood script by writers who know what they're doing. All of this is carefully wrapped in a beribboned package by a canny director.

In other words, it goes down easy.

But this is also a movie based on formula. Before seeing it, one could easily make several plot predictions. A) Demi Moore, playing a Naval officer intent on being the first woman allowed to undergo the famously grueling Navy SEALs training, will show off her muscles and complete the training. B) Her character's presence will elicit the resentment of her male chauvinist colleagues-in-training. C) Her plucky determination and refusal to accept special treatment will gradually earn her the grudging respect of the above. D) And a crusty drill sergeant (in this case the master chief played by Viggo Mortensen) will disdain and then admire her for her perseverance and heroism.

Under the direction of the experienced director Ridley Scott (Blade Runner, Alien, Thelma & Louise), the movie is as slick and seamless as a Hollywood movie can be. Directors strive for this forward momentum tug. But what catches in your craw are some of the movie's basic premises. Isn't heroism under fire only really admirable if it's achieved unwillingly? That is, aren't the best soldiers the ones who hate war and only engage in it to defend such lofty ideals as democracy and the low price of oil?

Anyone who wants to be a soldier because playing with guns is fun or because battle is exciting is missing one of the essential ingredients of a true hero - good sense. So, in the old days of the last noble war, World War II, when men were drafted to serve their country, those civilians unhappily left their families, donned uniforms and went to war because they had to and because it was the right thing to do. Not because they thought it would be enjoyable. Anyone who wants to go to war ought to be embarrassed to admit it.

So when Demi Moore's character, Lt. Jordan O'Neil, asks for active duty during the Gulf War, one wonders what her reasons are. Anyway, she is turned down. Now, owing to back-room political plotting by a grandstanding Texas senator, Lillian DeHaven (played deliciously by Anne Bancroft), the man who wants to be confirmed as secretary of Defense has agreed to allow a woman to train with the Navy SEALs, the elite covert operations unit.

But the fix is in. Defense is only allowing this little experiment in order to seem sympathetic to feminist views. In fact, since 60 percent of the male trainees drop out of the SEALs' basic training, everyone agrees that no woman thrown to these lions will last longer than a week. And when the military bases in DeHaven's state are threatened with closing unless she guarantees O'Neil's failure, the senator sabotages her charge's position.

This is pretty darn annoying after we've seen what poor Jordan went through for weeks to keep up with the boys. Never mind that she shaves off her pesky brunette mane to attest to her seriousness and improve her vision. Scott's brutal renderings of the abuse the soldiers take in the toughening process is persuasive. Twenty-hour days of physical exertion, with dinners eaten from garbage cans while officers yell to eat faster, well, it's enough to make you want to take two Advil and see the rest of the movie in the morning.

Moore sweats through the training grimacing and polishing her abs. She is in fine shape. She has lovely deltoids, too. She can do one-handed push-ups. And just to assure us that her character is a red-blooded all-American girl and not some patriotism-threatening, steroid-chewing lesbian, Jordan has a boyfriend, a naval officer (Jason Beghe) who doesn't get much to do here but fret at her career choice.

The most refreshing performance is by Mortensen as her commanding officer. He espouses the usual military-sadism spiel, including excusing apparent cruelty with the explanation that it saves lives. Mortensen, who appeared in Portrait of a Lady and Crimson Tide, has rarely looked so sleek, appealing and ready to play romantic leads as he does this time, gleaming out from behind a clipped mustache and a dangerous attitude. This ought to launch his career into the highest spheres.