Los Angeles — This is not the year to be Tommy Lasorda, Manager of the faded-blue Los Angeles Dodgers. Picked by most experts to repeat their division championship of 1983 in the National League West, the Dodgers, except for the injured Tom Niedenfuer, simply don't have a bullpen. They haven't been a whole lot better in the field, either, and the player they call the franchise (power-packed Pedro Guerrero) has been fighting a batting slump and a weight problem all year. Moved from third base to right field halfway through the pennant race to spare him the embarrassment of a possible 30-error season, Guerrero attributes some of his problems to an injured knee that he says limits his ability to wheel on a ball. Pedro is currently on the club's disabled list.
For Lasorda, who is reluctant to admit that both the San Diego Padres and the Atlanta Braves have better personnel right now than the Dodgers, 1984 has been a nightmare. In his efforts to get things started, Tommy has tried the conventional and the unconventional, including 71 different lineups in the Dodgers' first 100 games. Recently Lasorda allowed pitcher Orel Hershiser to bat for himself against the Braves with the score tied and several of his reserves available to pinch hit. Hershiser was retired easily.
However, not everything has been on the downside for Los Angeles this season. Hershiser, whose sinker is equipped with a passport to China, has become one of the best young pitchers in the league. In July alone, Orel pitched three two-hitters. Alejandro Pena, who won 13 games last year for LA, has at least an outside chance to make it 15 in '84. And the Dodgers are probably going to finish the season with four of their young hopes for the future (shortstop Dave Anderson, third baseman German Rivera, first baseman Franklin Stubbs, and outfielder R. J. Reynolds) in the starting lineup.
Even though hindsight is admittedly better than foresight, Lasorda might have kept the Dodgers in the race longer if, at the first sign that his bullpen didn't have it, he had pulled Fernando Valenzuela out of the starting rotation and turned him into a relief pitcher for the rest of the season. If nothing else , this would have taken a lot of pressure off Niedenfuer, who for a while was being asked to handle almost every late-inning situation that involved runners on base. Elsewhere around the major leagues
* The Chicago Cubs, who tightened up the National League West race by sweeping a weekend doubleheader from the first-place New York Mets, are not apt to fade down the stretch, according to Manager Jim Frey. ''We've always had the hitting,'' Frey says,''and now we've also got the pitching and defense to back it up.''
* Detroit's bullpen is on a pace that could make it only the fifth such unit in American League history to log 50 saves in a season. Fireman Willie Hernandez, Aurelio Lopez, and Doug Bair were involed in 52 of the Tigers' first 68 victories via 35 saves plus a 17-1 one-loss record.
* The Montreal Expos have acquired first baseman Dan Driessen in a trade with Cincinatti. Dreissen, a lifetime .270 hitter who was playing out his option year , has signed a new three-year contract with the Braves.
* The Chicago White Sox, who had won seven straight games prior to the All-Star break, now can't seem to find a stopper on a pitching staff that was once considered to have the best four-man rotation in baseball. For example, ace right-hander Richard Dotson, who was 11-4 on July 10, has allowed 17 earned- runs in his last 142/3 innings while going 0-3.