The biopic genre often is not easily executed. A director often shuffles between the demands of scrupulous historical accuracy and the need for a marketable, viable vehicle of entertainment in telling a story that must reflect the appropriate themes and epiphanies of that individual’s life. The film’s leading star must be careful to shade the subject’s role with just enough sophisticated nuance so as not to appear a parody and to suggest a reasonable, credible portrayal. The film’s screenplay writer must weave worthy, relevant bits of research into the script so that the voices are authentic in dialogue.

“Milk,” written by Dustin Lance Black, directed by Gus Van Sant, and headed in cast by Sean Penn, exceeds on all requirements. The story of Harvey Milk, the first openly gay elected public official in the United States and a San Francisco city supervisor who was shot to death along with Mayor George Moscone in 1978, is told with a keen eye zeroing in on the man’s innate, profound sense of history.

The film benefits significantly from Black’s research as well as his genuine appreciation of Milk’s historical importance. This was no easy task as one of the best sources — The Mayor of Castro Street, the 1984 biography by the late journalist Randy Shilts — has already been snapped up for a forthcoming documentary. Indeed, Black only became familiar with Milk’s story, long after the assassination, as a gay Mormon teen who moved with his family from Texas to San Francisco. Black, a writer whose credits are growing steadily (including HBO’s “Big Love”), started the project a few years back after interviewing some of Milk’s closest associates, long before any studio had expressed an interest in taking on the script as a viable property.

The film covers just six years, from the time, in 1972, when Milk moved from New York City to San Francisco up to the assassination in November, 1978. The film’s narrative is founded on Milk’s political will and testament, which he dictated into a cassette recorder shortly after his ground-breaking election in 1977. And, that is how the film begins with Milk (played by Penn in clearly one of the most earnestly crafted performances that has been seen in an American movie this year). He is in his kitchen late night in his Castro District home, creating the most critical artifact that will come to define his legacy.

This brilliantly executed opening, by virtue of foreshadowing, brings the audience fully into the story. Meshed intricately into the film are wonderfully orchestrated passages of archival news footage, including, most memorably, Anita Bryant, who is best remembered for her singular campaign in 1977 to defeat a gay rights ordinance in Miami-Dade County. There also is John Briggs, the California state senator who, in 1978, promoted a statewide initiative that would have barred gays and those publicly supporting gays from teaching in public schools. The Briggs Initiative, as it came to be called, was the defining political moment for Milk, whose speeches helped propel the momentum to have the initiative defeated resoundingly at the polls.

Black deftly situates these opponents in their own words, taking great care not to promulgate any buffoonish portrayals or parodies. And, with Van Sant’s direction, this critically opens the way for Milk to emerge on his merits as a leader who transcends the discourse of politics and campaigning. Ultimately, he is a leader at the height of his powers when he was tragically cut down. Rob Epstein, who directed the 1984 Oscar-winning documentary about Milk, says the Briggs Initiative campaign allowed Milk to prove that he was more than an “elected gay official.” This perception is consistent in this new film.

The culminating speech of that particular campaign comes alive in the hands of Black and in its delivery by Penn. Milk’s words are worth quoting in some length here:

“We must destroy the myths once and for all, shatter them. We must continue to speak out, and most importantly, most importantly, every gay person must come out. As difficult as it is you must tell your immediate family, you must tell your relatives, you must tell your friends, if indeed they are your friends, you must tell your neighbors, you must tell the people you work with, you must tell the people in the stores you shop in, and once they realize that we are indeed their children, that we are indeed everywhere, every myth, every lie, every innuendo will be destroyed once and for all. And once you do, you will feel so much better.”

Thirty years after the fact, the film reminds us just how striking Milk’s words were. And, even more striking is how timely they are in the still-unsettled dust of the fiasco that let victory slip earlier this month from the hands of marriage equality supporters in California. Watching the film also should jolt every individual directly invested in the gay rights movement about the leadership void that persists painfully. There is easy consensus that there is no defining leadership in this movement today.

To borrow David Remnick’s masterfully presented metaphors from a recent New Yorker piece that examined race and the Obama presidential campaign, Milk was among the pre-eminent figures of the “Moses Generation” of the gay rights movement. The parallels are unmistakable. Remnick, quoting Obama, summarizes: “the men and the women of the movement, who marched and suffered but, who, in many cases, ‘didn’t cross over the river to see the Promised Land.’”

And, as Obama said in that pivotal speech in the late winter of 2007 at a Methodist church in Selma, Alabama, “Milk” ultimately suggests the same question concerning the “Joshua Generation” of the civil rights movement. Remnick asks, “What’s called of us?” And, Black’s screenplay proposes the question in equally dramatic power to those who have inherited Milk’s mantle and who undoubtedly will watch this film.

I shudder a bit at the prospect that many gay rights group are planning to use the forthcoming screenings of the movie as public relations platforms to canvass support for marriage equality. These activities should be cast more subtly, as gentle approaches, because otherwise this could stunt the film’s potentially broad mainstream appeal. More than any other emphasis, the force of history is what drives this film. Folly comes to those who ignore history.

Milk is an important evolution in mainstream films that have gay-themed subjects. With “Philadelphia,” the presence of Tom Hanks and Denzel Washington brought the drama of AIDS into focus. With “Brokeback Mountain,” Ang Lee demonstrated that mainstream audiences were ready and comfortable with a love story involving two men, sensitively portrayed by Heath Ledger and Jake Gyllenhaal. Now, with “Milk,” we have the sufficient distance of 30 years to affix the proper historical parallels to our contemporary challenges.

Black’s script strikes the harmonious chords of hope that seem just right. Markos Moulitsas, the head of the Daily Kos empire, said as much in the days after the Prop 8 fight: “California will have marriage equality back soon enough — either this week if the Supreme Court takes action, or the next time we have an election in the state (either 2010 or next year if a special election is called). But I suspect history will show that the defeat of Prop 8, rather than halt momentum toward marriage equality (as I once feared), will prove the spark that launches the movement nationwide.”

Milk’s death was not in vain, as eloquently presented in the film. For a young writer, Black’s sense of history has that right tinge of patience. As Epstein noted, “while we may not be able to predict from where or when real leaders come, eventually they do. In the meantime, as we celebrate the election of a man whose own parents’ interracial marriage would not have been legal in sixteen states prior to 1967, Harvey, we’re still waiting.”

And, “Milk” may help spark that flame.

Van Sant’s direction is exceptional as always even with a film that is among the most conventional he has made recently. The supporting cast is equally up to the task, including Emile Hirsch, James Franco, Diego Luna, and, Josh Brolin, who stands out particularly as Dan Brown, the city supervisor who killed both men.

The only weakness of any consequence in the film is the sub story line involving Luna’s character, a cloying immature Hispanic lover. Its context was only partially developed to any satisfaction regarding its place in the overall narrative. Nevertheless, the film’s pace remains tightly choreographed.