LOS ANGELES — For System of a Down, the hard part of making their second album isn't the songwriting or the recording — it's the weeding-out process.

The Los Angeles rockers are in the midst of recording 32 songs, with the task ahead of cutting them down to a 12- or 13-track album.

"It's actually going to be tougher to do that than [anything else]," frontman Serj Tankian said last week. "Definitely you want the best songs, but you also want the songs to dance together — it's got to have some kind of common denominator running through."

Rick Rubin, who produced System of a Down's 1998 self-titled debut and is also at the controls for the new one, said the as-yet-untitled LP will be "almost like the greatest hits of two albums."

Though they spent months writing the material, Tankian, guitarist Daron Malakian, bassist Shavo Odadjian and drummer John Dolmayan have taken half the time to record twice as many songs as they did for their debut. They plan to mix all the tunes, so that they can use the remaining tracks as B-sides and for other projects.

Among the songs contending for the album are "Prison Song," "K.I.T.T.," "Psycho," "X," "Pictures," "Shame," "Chicken Stew," "Inner Vision" and "Shimmy."

Tankian said the album, which is expected midsummer, musically is "more classic. ... The heavy is really heavy, and the mellow goes to some beautiful places."

Rubin and Tankian attributed the growth that is showing up in the studio this time around to the two years the band spent on the road supporting its debut.

"Something happened over the past two years of singing onstage every night where Serj has become a tremendous singer," Rubin said. "There's way more vocal melody on the album. There's lots of harmony with Serj and Daron singing together — these beautiful, melancholic melodies that really expand the vision of what System was. It has all the qualities that we liked from their debut, plus this kind of tremendous musical growth. It's really very exciting for me to see. It's worlds apart."

The themes of the new material range from heavy political topics, such as the U.S. prison system, to spiritual sentiments as well as goofy subjects, like pajamas and the '80s television show "Knight Rider."

"There's definitely a really quirky vibe to some of the songs," Tankian said. "There's also stuff that's not so definable, as far as themes, that you've got to just explore and figure out for yourself — which I like."

Rubin added, "I think they've always wanted to be well-rounded lyrically, and not be thought of as just a political group. They really mix it up, in the same way of a band like the Clash — they didn't only sing about politics; they sang love songs and rock songs and reggae songs and blues songs."

System of a Down will tour this summer but have made no specific plans.