Keppinger, who hit .256 with seven homers and 29 RBIs last year, will make $1.15 million this season, and Sampson, who went 4-2 with a 5.04 ERA in 49 appearances, signed for $815,000 plus bonuses.
"We're pleased to get these two guys done, and we hope to continue to make progress on the others," Astros general manager Ed Wade said.
The Astros' remaining six arbitration-eligible players are center fielder Michael Bourn, right-fielder Hunter Pence, catcher Humberto Quintero and pitchers Wandy Rodriguez, Tim Byrdak and Matt Lindstrom, who was acquired in a trade from Florida last month.
The players and the team will exchange salary figures Tuesday and can negotiate deals before going to an arbitration hearing next month, where a panel will decide on either the player's figure or the team's offer.
"We'd love to get them done sooner rather than later and have the focus on getting to Spring Training and preparing for the season," Wade said. "But this is the time of year these things occur, and [assistant general managers] Ricky Bennett and David Gottfried want to stay focused on trying to get negotiated settlements, and if that doesn't work out [president of baseball operations] Tal [Smith] is working on the cases."
Bourn, Pence and Rodriguez were three of the Astros' best players in 2009 and will likely command large raises.
Bourn, who made $435,000 last year, was named the team's Most Valuable Player after setting career highs in at-bats (606), runs (97), hits (173), doubles (27), triples (12), RBIs (35) and walks (63) and led the National League with 61 stolen bases while batting .285.
Pence, who earned $439,000 in 2009, made the National League All-Star team and hit .282 with a career-high 165 hits, 14 stolen bases, 58 walks and 159 games. He led all Major League outfielders with 16 assists. Bourn and Pence are eligible for arbitration for the first time.
Rodriguez, who made $1.5 million last year, set career highs in wins (14), games started (33), innings pitched (205 2/3) and strikeouts (193) and posted a career-best 3.02 ERA. He led the Astros' pitching staff in wins, ERA, strikeouts and innings.
Lindstrom, Quintero and Rodriguez are eligible for arbitration for the second time, and Byrdak for the third time.
Keppinger, 29, hit .256 in 107 games in 2009 with 13 doubles, three triples, seven home runs and 29 RBIs after being acquired from Cincinnati on March 31. He had a combined 76 starts at third base, second base and shortstop. He has a .279 career average in 350 Major League games and a .341 career average against left-handers, which ranks ninth among active players.
Sampson, 31, was 4-2 in 49 relief appearances in 2009 with a 5.02 ERA with three saves. Sampson had a solid start to the season, posting a 4-0 mark in 36 appearances through June 26 with a 2.09 ERA and three saves, ranking among the league leaders in relief wins and innings before being slowed by discomfort in his right shoulder, which landed him on the disabled list from July 10-26.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.