As rumored, Tommy Lee Jones will act in Captain America: The First Avenger in a still-unknown role. Hayley Atwell, who plays Peggy Carter in the Joe Johnston-directed comic book adaptation, confirmed the news to LeicesterSquareTV. You can watch their interview with Atwell using the player below. They start talking about "Captain America" around the 2:20 mark.
Rumors place the "Men in Black" star in the part of General Chester Phillips, the military officer who chooses Steve Rogers for the super soldier program and who aided in his training soon after the serum took effect.
Phillips was retconned into continuity in "Tales of Suspense #63" in 1965, just two years after Captain America was brought to Marvel's forefront as the leader of the Avengers. Phillips remained a character in the Marvel universe until 2003 when he (now retired) was killed by assassins from the underwater rival-to-Atlantis continent Lemuria.
In addition to Atwell, Jones is joining Chris Evans, Hugo Weaving, Sebastian Stan, Toby Jones, Samuel L. Jackson and Dominic Cooper in the July 22, 2011 release.