Linehan had an 11-25 record in his first head coaching job. The Rams have been outscored, 147-43, this season, and have allowed at least 30 points in seven straight games dating to last year.
The move was made heading into the Rams' bye week and several hours after the Buffalo Bills outscored them, 25-0, in the second half of a 31-14 victory Sunday.
St. Louis has lost 17 of its last 20 games.
"This is not really the way you want to become a head coach, at somebody else's expense," Haslett said. "I feel for him and his family.
"We're going to do the best we can to try to get this thing turned around."
One big change under Haslett: practices will be open to media. Linehan closed workouts after the first 20 minutes.
"You can watch practice, you can be on the field," Haslett said. "You're not going to see anything you don't see in any other game."
The 0-4 start is the second straight for the Rams, who lost their first eight games last year en route to a 3-13 finish that landed them the second pick in the draft.
Haslett was fired as coach of New Orleans after the 2005 season, and joined the Rams on Linehan's first staff in 2006. Rick Venturi, assistant head coach and linebackers coach, was elevated to defensive coordinator.
No matter how dire the Rams' situation appears, Haslett said it'll never be as bad as in his final season as head coach of the Saints in 2005 in the aftermath of Hurricane Katrina.
"This is nothing compared to that," Haslett said.
Jet suspended for hit
Hours after Arizona coach
Ken Whisenhunt called for the NFL to review a helmet-to-helmet hit by New York's
Eric Smith on Cardinals receiver
Anquan Boldin, the Jets safety was suspended for one game.
Boldin was resting at home one day after being carted off the field in the Cardinals' 56-35 loss to the Jets in New Jersey.
Smith also was fined $50,000 for a flagrant violation of player safety rules, the league said.
Whisenhunt said he believed the hit violated the safety edict issued by NFL commissioner Roger Goodell, but he stopped short of calling for Smith to be suspended.
