Erstad, an outfielder, has signed a one-year, $1.75 million extension plus bonuses, and Moehler, a right-handed pitcher, signed a $2.3 million extension plus bonuses.
"We just thought that if we had a chance to move it forward we'd take advantage of it," said general manager Ed Wade. "They both epitomize the professionalism that we pride ourselves on and also are very talented guys. Their presence on the club speaks for itself."
Moehler, who was awarded a starting position in June, has an option for 2010.
The option includes different trigger events which would allow either him or the Astros to decline to renew the contract.
Moehler has been a surprisingly stable starter for Houston after barely making the team's roster. He is 9-5 with a 3.99 ERA in 25 games this season, with 20 starts, and had a five-game winning streak from July 9 to Aug. 19. The Astros are 13-7 when Moehler starts, and he is 4-1 in eight starts since the All-Star break.
"On the last day of Spring Training, in the clubhouse, we were talking about trying to get an advanced consent to go to the Minors if the time came during the season, and here we are five months later announcing an extension on his contract," Wade said.
A lot of the success, Moehler said, had to do with his finally being healthy after appearing in 29 games in 2006 with Florida. Between 2001 and 2003, Moehler appeared in just 17 games.
"I figured out what I need to do in the offseason," he said. "If I could take a few years back 10 years ago, I think I was a little too much into the weight room, and I've gotten away from that and trimmed down. I just feel better. I never forgot how to pitch. I'm comfortable and having fun again."
Wade said whether Moehler was given a spot in the rotation was up to the pitcher's performance next season.
"He's a member of the staff," Wade said. "What he does remains to be seen -- that's up to him to continue to put his best foot forward. There's no promises, other than he gets paid on the first and fifteenth next year."
But Moehler said he will still report to Kissimmee, Fla., with the mindset that he has to fight for a spot on the roster.
"I've always felt like even going into Spring Training, you've got to be ready to pitch and win a job," he said. "I've still got some work to do this year, and I'm looking forward to next year, as well."
Erstad, 34, has played all over the outfield and has 12 appearances at first base for the Astros. He is batting .293 with three home runs and 26 RBIs in 118 games this season, and is hitting .345 with runners in scoring position.
"We knew going in the character, the work ethic and professionalism that he's shown throughout his entire career," Wade said. "With some of the struggles we've had with some of the other outfielders, with [Michael] Bourn struggling in the early stages of his career and Carlos [Lee] going down, I don't know where we would be without Darin, from the standpoint of his playing ablility. From the standpoint of his clubhouse presence, he fits perfectly with the blueprint that we tried to put together for quality guys in the club."
Erstad said the same thing about the club, calling the Astros a class act of which he was proud to be a part.
He said the adjustment from being an everyday player with the Angels and White Sox was difficult, but something he enjoys now.
"It was time in my career for a different role, and the guys we have on the team make it a lot easier, because you want to pull for them. You want to pick them up because they play hard."
Erstad was out for the majority of the 2005 and 2006 seasons with injuries.
Both players were to be free agents at the end of the 2008 season.
Krysten Oliphant is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.