The Los Angeles Rams are never flashy, always relentless. Tonight, they defeated the Chicago Bears, 20-17, at Soldier Field when Mike Lansford kicked a 50-yard field goal with four seconds to play.

It was as if, all at once, the Rams' passing ills were cured. Their quarterback, Steve Dils, had completed only three of 20 passes against the league's most feared defense in the game's first 59 minutes and 13 seconds.

But in the last 47 seconds, he coolly drove the Rams 33 yards, completing three of five passes, to arrange for Lansford's heroics. The kick stunned the sellout of 64,877, ended the Bears' 14-game home victory string and left both teams 7-2.

The victory was nearly monumental to the Rams, who opened a 1 1/2-game lead over San Francisco and Atlanta (both 5-3-1) in the NFC West division. Their all-pro running back, Eric Dickerson, ran for 111 yards on 29 carries; their all-pro cornerback LeRoy Irvin picked up a fumble by Bears punter Maury Buford and ran 22 yards for a third-quarter touchdown, and their defense put in another yeoman effort, limiting the Bears to 269 total yards.

"You can say we're one-dimensional and all that stuff," said Rams Coach John Robinson, "and I say: 'So what?' "

For the Bears, the loss merely means their lead over Minnesota (5-4) in the NFC Central remains at two games. The loss also reaffirmed the shiny truth that, without sidelined quarterback Jim McMahon, the Bears are an entirely beatable bunch. Backup Steve Fuller completed only nine of 19 passes for 102 yards with two interceptions, before being replaced by Mike Tomczak (two for eight for 25 yards) with the score tied at 17 late in the third quarter.

"We've gone down a tough road so far this year with all of the turmoil and injuries," said Bears linebacker Mike Singletary. "We've been through a lot and still managed to win. We lost tonight, but it isn't going to dampen my spirits . . . I know one thing: we're going to be all right. I know that."

The Bears have won the last 22 games McMahon has started, but they aren't certain when his sore shoulder will be well.

The Bears played the last quarter without record-breaking running back Walter Payton, who dislocated a toe in the third quarter, after having run for 61 yards on 19 carries. (The severity of Payton's injury was uncertain.)

Then again, the Bears didn't seem to miss Sir Sweetness. His replacement, second-year man Thomas Sanders, ran for two touchdowns, measuring 10 yards and 34 yards, in the third quarter. This not only stemmed the Rams' tide when they awoke from their first-half slumber, but it gave the Bears a 17-10 edge with 4:23 left in the period.

The Bears led, 3-0, after a fretfully slow and uneventful first half. But the world turned over several times in the third quarter. Three touchdowns were scored during one stretch of less than 2 1/2 minutes.

The Bears began the quarter by stuffing Dickerson on fourth and one from the Chicago 33. Defensive tackle Steve (Mongo) McMichael put the hit on Dickerson, who fumbled. Safety Dave Duerson recovered.

This blown opportunity for the Rams blew back in two plays later when Fuller's pass to Payton in the right flat was intercepted by safety Jerry Gray at the Chicago 32. Gray returned it 18 yards.

Naturally, the Rams' offense managed only five yards in three plays and settled for Lansford's 26-yard field goal, tying the score at 3 with 9:45 left in the third quarter.

The Bears seemed momentarily to come apart at the seams. On their next series, Buford went in punt formation from his 32. The Rams' Irvin was virtually unblocked and came through the right side. Buford had no time to punt, so he ran to his right.

He was hit by linebacker Jim Laughlin and made his first fumble in five years in the NFL. Irvin scooped it up and ran 22 yards for the touchdown that gave the Rams a 10-3 lead.

It was at this point the Bears realized that Payton was injured and unavailable for the rest of the game. In four quick plays, the Bears turned the game around.

First, Dennis Gentry ran 84 yards with the kickoff. Mark Jerue finally caught him at the 15. Sanders soon followed with his 10-yard touchdown run through the left side. The Bears were back even at 10 with 5:46 left in the quarter.

Then veteran safety Gary Fencik made his 37th career interception (tying Richie Petitbon's club record), making an eight-yard return to the Rams' 34.

Just like that, Sanders swept around the right side, blew past safety Johnnie Johnson at the 25, and went 34 yards for the 17-10 touchdown.

"I thought, if we got up on them, we would beat them," Bears Coach Mike Ditka said, "but we didn't do it."

Dils later passed to wide receiver/Olympic sprinter Ron Brown for a 65-yard touchdown. Brown left cornerback Shaun Gayle in his wake, and the score was tied at 17 with 1:28 left in the third quarter.

There had been great anticipation about this game. It was, after all, a rematch of last season's NFC title game (won by the Bears, 24-0). You had a matchup of running backs extraordinaires, Dickerson versus Payton, and maybe even the Rams' yet-to-play rookie quarterback Jim Everett versus the Bears' recently signed Doug Flutie, formerly of the U.S. Football League.

Of course, the Bears did not activate Flutie today. (They will do so on Monday or they must waive him.) Maybe that's the reason that, before the game, a security guard pulled down the bedsheet banner in Soldier Field that proclaimed: "It's Howdy Flutie Time."