Ivory Sully blocked a 24-yard field goal by San Francisco's Ray Wersching with 1:53 remaining to save the 9 1/2-point underdog Los Angeles Rams a 21-20 victory today and deprive the 49ers, last season's Super Bowl champions, of a spot in the NFL playoffs.

The 49ers would have stayed alive at 4-5, but ended 3-6; the Rams 2-7.

The 49ers drove from their 25-yard line to the Rams' seven in the closing minutes and called on Wersching, who had missed an extra point in the second quarter. Wersching's kick was low and Sully, diving to his left, knocked it down at about the line of scrimmage.

Wendell Tyler, who scored two Los Angeles touchdowns, clinched the game by running 54 yards, to the San Francisco 26, on third and 10 after the 49ers' final timeout.

The Rams, who had blown several big leads this season, won after trailing at halftime, 20-7.

Wersching, a hero in Super Bowl XVI, missed his extra point after Joe Montana's 29-yard pass to former Maryland track star Renaldo Nehemiah gave the 49ers the 20-7 lead.

Los Angeles' Vince Ferragamo found George Farmer for a 41-yard completion as the Rams drove 77 yards for a touchdown, scored by Tyler on a one-yard run, in the third period. Ferragamo threw 42 yards to Farmer for another touchdown with 8:59 left in the game. Mike Lansford added the winning extra point.