Julia Roberts is a $20 million woman for a reason. There’s something absolutely luminous about her screen presence; she could be interesting to watch even if she weren’t a good actress, which, luckily enough for movie-goers, she is.

In her latest film, “Erin Brockovich,” Roberts proves her acting chops in relatively fine form. The film is a true story about a small law firm that played out a David-and-Goliath scenario with billion-dollar juggernaut Pacific Gas & Electric Company.

The real-life Brockovich makes a quick appearance in the movie as a waitress wearing, in a bit of ironic humor, a name tag that reads “Julia.”

For those who think of Roberts as America’s Sweetheart, “Brockovich” sends a blow to that image. In other words, Roberts’ character doesn’t get a “Pretty Woman”-style makeover during the course of the film. Erin Brockovich is tough-talking. She’s been married twice and has three young rugrats.

Erin’s got an interesting style of dress. Indeed, much has been made of the fact that Roberts’ usually low-key cleavage basically acts as another co-star in the film.

She wears pedal pushers and mini-skirts.

She says the f-word a lot.

She doesn’t apologize for who she is, which is a single, working-class mother with no education but plenty of ambition.

Roberts’ Brockovich is down on her luck. She’s utterly broke, and within minutes of the opening credits, she gets into a car accident and winds up in a neck brace. Erin goes to a small Los Angeles law firm, where she’s represented by Ed (Albert Finney, “Tom Jones.”)

After Erin spews forth some profanity while on the stand, she loses her case but bulldozes Ed into giving her a job filing papers at the firm.

While going through some real estate records of the nearby small community of Hinkley, Erin notices there are medical records of some of the townspeople in the files.

With Ed’s permission, Erin drives to Hinkley to investigate. What she finds is that the Pacific Gas & Electric Company knowingly allowed high levels of toxic chromium seep into the town’s water supply. As a result, hundreds of the townspeople are getting deathly ill.

Because of the connection Erin makes with Hinkley’s residents that stuffy lawyers could never manage, she manages to rustle up more than 600 people willing to file suit against PG & E.

While Erin is working hard on the people’s case, she starts to earn the respect of her co-workers, and she’s doing something that she can be proud of professionally for the first time in her life. However, on the homefront, Erin’s personal life is suffering, as she’s rarely seeing her kids and her Harley Davidson-riding beau, George (Aaron Eckhardt, “In the Company of Men”).

Also, Erin’s getting some weird, threatening phone calls about people warning her to stay away from the case.

However, Erin’s committed and doesn’t for one scene show an iota of apprehension, which is good considering how often members of the law firm want to compromise on the plantiffs’ case.

Roberts’ star quality often precedes her performance. Despite the press-on nails and see-through tops, she’s still Julia Roberts, unarguably the most powerful actress in Hollywood. But she triumphs in spite of this; her performance as Erin comes across as tough, resourceful and ultimately very human and compassionate.

Finney also does an excellent job as Roberts’ straightman; he’s appropriately befuddled, and the friendship and mutual trust that develops between him and Erin is one of the strongest points of the film.

Some have pointed out that “Erin Brockovich” is similar to director Steven Soderbergh’s last effort, “A Civil Action,” where John Travolta’s lawyer also took on a company that was poisoning residents.

However, this story is multi-layered, evenly balancing the tales of the victims, Erin’s unrelenting commitment to those people and a touch of feminism — when she seemingly must choose between her boyfriend and her cause.

For a fairly lengthy film (two-hours-plus), the pace seems just about right, and Roberts, although she seems a bit out of place in a few scenes, still delivers in what’s been the best role of her career.

4 1/2 Stars.

Rating based on a 5 Star scale.