“Brokeback Mountain” strengthened its claim as the Academy Award front-runner, while dark-horse “Crash” came on strong and George Clooney made history at the nominations announced Tuesday.

The star-crossed cowboys of “Brokeback Mountain” emerged as Oscar trailblazers, the story of doomed love between two men poised to become the first gay-themed film to lasso the top prize.

With a leading eight nominations, “Brokeback Mountain” is the clear favorite to win best picture.

The film also picked up acting nominations for Heath Ledger, Michelle Williams and Jake Gyllenhaal and a directing nomination for Ang Lee.

Besides “Brokeback Mountain,” other films from the independent world dominated the field, with Steven Spielberg’s assassination thriller “Munich” the only big-studio film to score a best picture nomination.

The other best picture nominees were the Truman Capote tale “Capote,” the ensemble drama “Crash” and the Edward R. Murrow story “Good Night, and Good Luck,” which Clooney directed.

The Oscar field often includes fluffier, happier films, but the lineup this time offers a wealth of challenging, stimulating stories.

“Things are being simplified a lot for us lately. I think people are hungry for something that shows more respect for the complexity of life, the depth, the gray areas,” “Brokeback Mountain” director Lee said.

“I think it’s fabulous that people want to be entertained but also want to have a mirror held up to the culture and be thought-provoked,” said Rachel Weisz, a supporting-actress nominee for “The Constant Gardener,” a murder thriller set against political and corporate corruption in Africa.

Along with directing and screenplay nominations for “Good Night, and Good Luck,” Clooney earned a supporting actor slot for the oil industry thriller “Syriana.”

His two movies were among the rush of nominees taking on political and social issues, a sign that Hollywood may be returning to a sense of activism not seen since the Watergate days in the ’70s, Clooney said.

“Honest to God, it’s a fun year,” said Clooney, who became the first to get directing and acting nominations for two different films in the same year. “What it comes down to is these two films, people worked really hard on both of them, and I thought both of them were pushing the needle, not as much socially and politically as people like to say, but in terms of what studios are willing to make.”

Spielberg, a best-director nominee for “Munich,” said Hollywood activism ebbs and flows, but hit a high point in 2005.

“I just think there’s a very courageous cultural surge occurring, and some of it could be political, some of it could be a response to the neoconservatism,” Spielberg said.

“Crash,” which follows a huge cast of intersecting characters over a tumultuous 36-hour period in Los Angeles, earned great reviews and had been a mini-hit but seemed as though it might be overlooked come Oscar time. It picked up steam as awards season progressed, culminating in a surprise win Sunday over “Brokeback Mountain” for the overall cast prize at the Screen Actors Guild Awards.

More often than not, the SAG cast winner does not go on to win the best-picture Oscar, and the dominance of “Brokeback Mountain” at Tuesday’s nominations and in earlier Hollywood honors such as the Golden Globes makes it the film to beat come Oscar night March 5.

Click to view complete list of Oscar nominees.