The meeting of Al Pacino and Robert De Niro in "Heat" is being touted as a real event, since the only other pairing of the two dynamic Oscar-winners was in "The Godfather, Part II" — and, of course, because De Niro played Pacino's father in flashbacks, they never shared the screen.

But in truth, they aren't on the screen together all that much in "Heat," either. Most of the time, Pacino, as an obsessive workaholic cop, is in the shadows as he tracks the labors of precision-professional thief De Niro and his gang.

Writer-director Michael Mann ("Last of the Mohicans," "Man-hunter," TV's "Miami Vice") means to do more here than simply offer a typical cops-'n'-robbers thriller. He wants to celebrate police procedure in realistic detail, show how difficult it is to be a cop and maintain a family, and he also wants to put on display the criminal's point of view.

To achieve this, Mann allows both Pacino and De Niro's characters equal time in a nearly three-hour film. Despite the excellent performances of the stars, however, it doesn't quite work because Mann's material is not consistently compelling enough to make it worthy of that unwieldy length. As a result, there is a really good two-hour movie struggling to get out of this pretty-good three-hour movie.

Still, fans of the two stars will probably find it worth their while.

Pacino plays Los Angeles police detective Vincent Hanna, on his third marriage, with a marijuana-smoking wife (Diane Venora) who is tired of his work obsessions and a stepdaughter who is seriously troubled because her real father neglects her.

De Niro is career criminal Neil McCauley, an ex-con who swears he'll never return to prison and who has organized his "crew" (Val Kilmer, Tom Sizemore and Jon Voight) to plot and execute a series of high-revenue robberies.

When one of the robberies goes wrong, thanks to an unreliable gang-member recruited at the last minute, Hanna scrapes up a few clues to help him track down some of McCauley's gang. In order to put them away permanently, however, Hanna needs to catch them in the act. So, he starts tracking their activities, with the assistance of his fellow police officers (including Wes Studi of "Last of the Mohicans" and "Geronimo" and Mykelti Williamson of "Forrest Gump").

There are some terrifically staged (if unrealistic) action scenes, at which Mann is most adept. And a highlight sequence has Pacino pulling De Niro over on the freeway and suggesting they discuss their perhaps unexpected similarities over a cup of coffee.

The supporting cast is also first-rate, though even in this three-hour epic, some (most notably Studi and Williamson) have little to do.

As a contemporary crime thriller, however, "Heat" is certainly more thoughtful than most, and despite a few somewhat sluggish moments, it doesn't really drag all that much. Too bad it isn't just a bit more emotionally involving.

"Heat" is rated R for violence, gore, sex, nudity, wall-to-wall profanity and vulgarity and drug abuse.