TORONTO - Carlos Peña hasn't lost his starting job. But the rookie first baseman's month-long slump is prompting changes in the A's lineup.

Saturday, he was not in the lineup for the second consecutive game and the fourth time in the past seven games. He started the previous 35 games.

The A's are keeping a close eye on Peña, who is 4 for 37 (.108) in his past 14 games and has gone 47 plate appearances without an RBI. He was the American League rookie of the month after hitting .264 with seven home runs and 16 RBIs in April. But the slump that has dropped his average to .223 has renewed concerns that Peña, who turned 24 Friday, might need more seasoning in the minors.

Peña is scheduled to start today. Although Olmedo Saenz and Scott Hatteberg started at first base on Friday and Saturday, respectively, Manager Art Howe said the position is not turning into a platoon.

``I'm just trying to give other guys an opportunity to play,'' Howe said. ``Obviously we've been having trouble scoring runs. I'm looking for the best combination production-wise that I can.''

A decision to send Peña to the minors won't be easy. He is the team's best defensive first baseman. Despite his struggles, Peña, who bats left-handed, is hitting .326 against left-handed pitchers.

``Young hitters go through those dips,'' hitting coach Thad Bosley said. ``He got off to a great start, and now he's gone through the little dip. Hopefully he's scraped the bottom and can get back up and level off, and if he does go down again, it won't be as huge.''