The Rays avoided salary arbitration with each with the contracts.
The contract for Bartlett, 30, is for $4 million and comes after he posted his best year as a pro, hitting .320 with 14 home runs, 66 runs batted in, 90 runs scored and 30 stolen bases.
Garza, 26, went 8-12 with a 3.95 earned run average in a career-high 32 starts in 2009. He also posted personal bests in innings pitched (203) and strikeouts (189). He will make $3.35 million this year.
Howell, a left-handed reliever, racked up a 7-5 record in 69 appearances for the Rays, registering 17 saves and a 2.84 ERA.