Jake Gyllenhaal should have no fears of typecasting.

Soon after finishing the gay cowboy romance “Brokeback Mountain,” he launched into the role of a young soldier thirsty for Gulf War action in “Jarhead.”

“Jarhead” will be released on DVD next week, right after the Oscars – in which “Brokeback Mountain” is a favorite and the 25-year-old Gyllenhaal is up for best supporting actor for his portrayal of a lovestruck sheepherder.

It’s a thrill for Gyllenhaal, who started his movie career at age 11, playing Billy Crystal’s son in “City Slickers.” Eight years later he was an aspiring teenage rocket scientist in “October Sky,” and he broke out in 2002 as Jennifer Aniston’s love interest in “The Good Girl.”

But the blue-eyed actor says his roles in “Jarhead” and “Brokeback” are among the most meaningful he’s played. Though he only had three months to go from gay cowboy to Marine recruit, he says the disparate characters are more similar than they seem.

AP: What was the transition like between these characters?

Gyllenhaal: There are a lot of physical differences and a lot of differences in terms of intention, but ultimately both of them come from parts of me. In that way, they’re the same, kind of. They both come from my heart and it’s the same derivation. There’s definitely a rage that (Jarhead’s) Tony Swofford, the character of Swofford, had that the character of Jack Twist doesn’t. He’s much more open and engaged, much less cynical.

AP: You went from horseback riding to boot camp. Talk about the physical differences.

Gyllenhaal: [“Brokeback” director Ang Lee] put a set of weights outside my trailer because he wanted me to kind of bulk up for that part. I tried my best but I didn’t do it as well as maybe he wanted. But then for “Jarhead,” it was sort of mandatory. So I spent those three months reading, and I started working out like really heavily.

AP: What appealed to you about these two roles?

Gyllenhaal: With “Jarhead,” it was just kind of like a perfect match. When you get to be a certain age and you’re learning how to be a man, there are probably physical, hormonal things and just, I don’t know, spiritual things that happen. The feeling of wanting to punch your fist through a wall and not understanding what that is. It’s just inherent in growing up. But that’s a real, legitimate feeling, and those feelings and that part just coincided perfectly. And there is a resistance in both of the characters. They’re not allowed to be their full selves, and I think that I was really drawn to that.