Scarily intense and shockingly immediate, the sex scene in Ang Lee's new film Brokeback Mountain hits us with gale force. We watch two ranch hands, Jack Twist (Jake Gyllenhaal) and Ennis Del Mar (Heath Ledger), huddling together in a dark tent. The wide-angle lens draws us very close to the actors; the hand-held camera allows the events to unfold in one continuous take.

The director says he knew the entire film depended on this scene -- that unless we experienced these heated moments right alongside Jack and Ennis, we couldn't possibly understand the tortured, decades-long romance between the men that follows.

"I think it's a very private moment, and I think it needs to be watched closely," Lee explains, during a telephone interview earlier this month. "But it has to be raw. You can't put too many pretty lights in there and make it too nice."

There's nothing nice here at all: The action starts out awkwardly, but quickly turns urgent, even frenzied. And while the images aren't especially explicit (there's no nudity), the actors' physical movements and the director's attention to detail leaves absolutely nothing to the imagination.

Brokeback Mountain (opening Friday in Dallas) is a momentous achievement: Partly because we haven't seen a love story this baldly emotional and sincere in decades. But mostly because Lee has taken two of Hollywood's most classical (and classically heterosexual) genres -- the Western and the doomed love affair movie -- and rewritten them in distinctly gay terms.

Yet Brokeback Mountain doesn't come out of the indie left field, the way you might expect for a film that charts 20-plus years in the lives of its closeted gay lovers. The director is the same man who made such award-friendly titles as The Ice Storm, Sense and Sensibility and Crouching Tiger, Hidden Dragon. The screenplay is by Pulitzer Prize-winning novelist Larry McMurtry (who collaborated with Diana Ossana). In perhaps the ultimate sign of mainstream embrace, the film is being talked up right alongside such traditional Oscar-bait as Memoirs of a Geisha and Walk the Line for a Best Picture nomination. (The Web site Movie City News -- which conducts weekly polls of a dozen awards pundits -- presently ranks it as the front-runner).

This is unlike anything we've seen before. Brokeback Mountain doesn't apologize for its gay characters and themes, the way so many Hollywood films have in the past. And, as evidenced by that blistering sex scene, it doesn't do anything to make heterosexual viewers especially comfortable, either.

Instead it takes as matter-of-fact the possibility that overpowering, all-consuming love can blossom between two men, and also that gays have just as strong a claim on classic stories and genres as straight moviegoers do. And it's for these reasons that this soft-spoken, melancholy drama -- set decades ago, deep in the American heartland, in Wyoming and Texas -- might just be the most trenchant and bracingly political movie we've seen in years.

To understand the impact of Brokeback Mountain, which is based on a 1997 short story by E. Annie Proulx, you need to understand where it's coming from: namely, a century's worth of Hollywood films that have treated gay people with derision and enmity at worst, and liberal condescension at best.

In the 1940s and '50s, gay characters tended to be either effeminate men who shuffled onto the screen to provide comic relief, or distressingly butch women who represented All That Is Evil. As for those rare sensitive treatments of gay characters -- William Wyler's adaptation of The Children's Hour (1961), for instance -- the homosexual content is buried so deeply between the lines that it takes a Ph.D. in English literature to sort out what's going on.

Gay men didn't even exist in leading parts until well into the 1970s -- and even then, in movies like Dog Day Afternoon (1975), where Al Pacino plays a man who robs a bank in order to secure his lover a sex change, their plights were made to seem outlandish, even campy; the weird and outre obsessions of a weird and outre class of people.

Philadelphia (1993), Jonathan Demme's landmark drama about a gay lawyer battling to die with dignity, permanently altered the landscape -- and since then we've certainly seen dozens of progressive, complex representations of gays and lesbians in movies and on television.

But for all that's affecting and true about Philadelphia, especially how it captures the ostracism of a successful gay man trying to flourish in a predominantly straight corporate world, it's also a movie that does everything possible to make certain that straight moviegoers do not feel threatened. The only intimation of sex between Tom Hanks' Andrew Beckett and his lover (played by Antonio Banderas), is a chaste slow dance at a costume party. Even the flashbacks hinting at how Beckett contracted HIV are cloudy and indirect, almost as if to shut down anyone who might suggest "he got what he asked for."

Brokeback Mountain, then, is to Philadelphia, what Do the Right Thing (1989) is to Guess Who's Coming to Dinner (1967) -- both a summation of everything that's come before it and a call-to-arms for the future. Philadelphia, with its portrait of a "saintly" gay man (not unlike Sidney Poitier's "Noble Negro" in Guess Who's Coming to Dinner), opened the door for dialogue about gay equality. Brokeback Mountain goes smashing through that door.

And it does this by refusing to soft-pedal its deeply flawed characters. After Jack and Ennis' blissful summer in Wyoming comes to an end, they each part ways, and head off to live "straight" lives -- Ennis marries a country girl named Alma (Michelle Williams), while Jack moves to Texas and marries Lureen (Anne Hathaway). The deception the two men carry on over the next two decades -- running off together two or three times a year, for a week at a time, carrying on right beneath their wives' noses -- isn't especially honorable. In the case of Jack, who is much more at ease with his sexuality than Ennis, his eye never stops wandering toward other men.

All of the classic "straight" paranoid ideas about gay people are being acknowledged here: that they replace love with sex; that they are deceitful; that they are incapable of monogamy.

Equality is often earned by proving you're better than the next guy. But a deeper equality comes when you've nothing to prove -- when society at large allows you to be just as much of a lout as the next guy.

Which is to say that Brokeback Mountain pays gay people a compliment they've never been paid before in a mainstream Hollywood movie: It lets them be human.

A few other things that mark Brokeback Mountain as one of a kind: It's a movie steeped in emotionalism from a filmmaker more commonly prone to hold viewers at a polite remove. It stars two up-and-coming, avowedly heterosexual actors who don't ask for hosannas for "playing gay" -- indeed, they hold absolutely nothing back when it comes time to deliver a wildly romantic, full-mouth kiss in the open daylight.

Most intriguing of all: It's composed of strikingly familiar images that, recast in a "queer" context, force us to reconsider our notions of the American West, and the American Western movie; classic love stories and the love story genre.

In the opening section of the film, Lee risks ridicule with a series of long, almost silent passages in which the two men work side by side on the mountainside -- it's an Abercrombie and Fitch ad with cute boys and sheep.

But Lee's patience with the camera, and especially the way he stands in awe of the landscape against which the drama unfolds, reminds us of those iconic images created by directors such as Howard Hawks and John Ford, in movies like Rio Bravo, Red River and The Man Who Shot Liberty Valance. Lee reminds us that our larger perception of the American West is bound up entirely in Westerns -- and those strutting masculine heroes played by the likes of John Wayne and Henry Fonda -- that we all grew up watching.

As a love story, Brokeback works much the same way. It is the first mainstream Hollywood film to suggest that, after decades of having to live vicariously through straight characters' doomed love stories, from An Affair To Remember to Sweet November, gays and lesbians are owed stories of their own.

This is the question that has been on the lips of journalists and film industry types since early September, when Brokeback Mountain screened at the Telluride, Venice and Toronto film festivals. The widespread perception among critics is that it's the best thing Lee has ever done and that the previously pretty boy-ish Ledger had been reborn as a potential Oscar winner.

But many have wondered if the mainstream is ready for a movie so bluntly matter-of-fact about gay life. Others have questioned if Brokeback Mountain will only serve to feed into the current backlash against gay marriage that's been witnessed at the polls over the past few elections.

Focus, the studio that's releasing the film, is treading very gently. The movie opened in New York, Los Angeles and San Francisco on Friday and will expand to 55 theaters this weekend. It's expected to open in Fort Worth on Jan. 6. The studio is counting on Golden Globe and Oscar nominations to push the film into wider release throughout January.

These are questions Lee isn't especially keen on addressing. "It might have political implications," he says, "but I hope [moviegoers] see beyond that."

At the same time, the director doesn't deny his fears that the movie could easily be hijacked by pundits on both sides of the political divide.

"I wish there were movies like this before me, so I don't have to be like the Marine, the one who goes forth and is the first one into battle," he says. "I'm not a politically driven filmmaker."

And Brokeback Mountain isn't an especially political movie, at least not on its surface. Despite the fact that much of the action takes place in the 1960s and '70s, we're never given a sense of the social changes happening in America at large -- mainly because Jack and Ennis have no sense of those changes.

But the thing that Brokeback Mountain understands so well is that the political is deeply bound up in the personal -- this is what raises the movie to the level of a masterpiece. Like Mike Leigh's abortion melodrama Vera Drake (2004), Brokeback lives completely in the day-to-day actions of its characters, who are decent-hearted, everyday souls who don't want to have to carry the burden of vast social change on their shoulders. It's only by implication -- by showing us how larger political realities can destroy the hopes and dreams of ordinary people -- that the film's message becomes unavoidable.

As many critics have already noted, the second half of Brokeback Mountain doesn't feel particularly gay or straight -- only agonizingly, heartbreakingly tragic. Jack and Ennis come together and break apart, again and again. Jack dreams of the two of them settling down on a ranch together somewhere. Ennis, who was raised by a homophobic, gay-bashing father, can't even begin to comprehend living with another man. The impasse they come to is one that transcends sexuality: It's the universal story of people driven apart by circumstance; of fighting against a system that refuses to budge an inch; of passion that isn't allowed true expression.

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