LOS ANGELES–There is an unwritten rule in Hollywood that if you are over 50 and your name isn't Meryl Streep, you won't be taking leading roles away from younger women. Finding work becomes even more difficult if you prefer not to play wives or mothers. Joan Allen, who turned 50 a year ago, is trying to be an exception to the rule.

She has done well thus far. In The Bourne Ultimatum, she brings back The Bourne Supremacy's Pamela Landy, the leader of a team of CIA operatives trying to track down renegade operative Jason Bourne. (The movie opens Friday, August 3.) Allen is no stranger to taking on women who roam the corridors of power, having won Oscar nominations for playing a U.S. candidate for vice-president in The Contender and a president's wife in Nixon.

In an L.A. hotel room, she says that she divides her personal acting history into two parts: the wives and mothers who support the lead male actor and the women who are a part of the action. "If you take The Ice Storm and The Crucible and Nixon–and even Pleasantville, to an extent–you have the wife and mother who is holding things together while also holding herself together. At the time that I was doing each one of them, I found them to be great experiences because of the variety. You are in the 1970s in the White House and then you are in 17th-century Salem [in The Crucible].

"But after Pleasantville, I felt that I had done that and I had done the best of that, because all the characters were very well realized and they were not ciphers. But I thought, 'If I see a script that you can describe [my role] as the wife or mother, then I am not going to do it, because I have been there and done that.' Fortunately, in the last few years–with this character [in the Bourne films] and with some indie films like The Upside of Anger and Off the Map–directors have trusted me and financiers have believed in me enough that they will give us the money. So, as a result, I have been able to expand my characters a lot."

Allen says that she is aware that the film industry is not particularly interested in sending a lot of leading-lady scripts to women her age and says that when the scripts become completely unacceptable she may take her career in another direction.

"There is a trend in television where you see women over 40 getting great roles in series work. People like Holly Hunter and Glenn Close are getting opportunities to play parts that are far more interesting than they would be getting in movies. And I am still getting scripts where I am asked to play someone's mom. So I like the TV thing. The Brits have done it for a long time. They have let women do interesting things in television, and I feel like that idea might be crossing the pond a little bit."