Because Tony La Russa's starting pitchers have been unable to get past the middle innings consistently this season, he has refused to let them try anymore.

The Oakland Athletics manager last night unveiled a platoon system for his starting rotation that he and pitching coach Dave Duncan have been sitting on since they first discussed it 11 years ago while with the Chicago White Sox.

La Russa, who has 13 pitchers on his active roster, scrapped the traditional five-man rotation for a nine-man rotation divided into three-man platoons. Todd Van Poppel, Ron Darling and Kelly Downs are in the first group; Mike Mohler, Bobby Witt and John Briscoe in the second; and Bob Welch, Shawn Hillegas and Rich Gossage in the third.

Dennis Eckersley remains the closer in a four-man bullpen.

Limiting each pitcher in the platoon to between 40 and 60 pitches, the system allows La Russa to send out each group on two days rest.

"It's an interesting shot to take," La Russa said. "We'll watch it real closely and see what happens."

The experiment began last night and worked - sort of - as the Athletics lost to the Cleveland Indians 4-2. That loss was far more palatable than the three straight by a composite score of 32-14 during the weekend in New York.

"Today it gave us a better shot as far as shutting down the other offense," La Russa said.

The A's have lost nine of their last 12 games and have not been above sixth place in the AL West since May 1. Oakland starters were 20-31 with a 5.43 earned-run average entering last night's game with only three complete games this season - all by Witt.

Van Poppel, a rookie, started and threw 50 pitches in four innings, allowed three runs on three hits in the first inning, and held the Indians hitless the next three innings.

But La Russa, true to the plan, inserted Darling for his first relief appearance since 1990, ending a string of 84 starts. Darling allowed a seventh-inning RBI single by Junior Ortiz, but only one other hit in four innings.

Because Van Poppel and Darling combined to throw fewer than 100 pitches, La Russa didn't use Downs.

Downs, he said, would go into the rotation for tonight's game, to be started by Mike Mohler.

La Russa denied the radical change was a sign he was giving up on winning the West Division title.

The A's are 11 games under .500.

"It's not a concession," he told the Oakland Tribune. "A concession is if you cover your(self) by doing nothing. We're in sixth place. . . . What are we jeopardizing?"

Don't ask Darling.

"I don't even mess with saying I truly understand what's going on," Darling said. "We have to stay ready to go, and then go until he taps us on the shoulder."

-------------------------------------------------------------. Oakland's mound malaise. .

-- Why did Manager Tony La Russa scrap Oakland's starting rotation for a nine-man platoon system? Here are seven reasons to start - and the numbers to show why La Russa isn't using them as traditional starters anymore. The results of Oakland starting pitchers in the team's 20 games before last night's change: .

GS IP H ER BB SO ERA W-L Team#. . Bobby Witt 4 27 2/3 34 17 5 18 5.53 1-3 1-3. . Kelly Downs 4 21 2/3 29 17 7 12 7.06 0-2 2-2. . Ron Darling 4 21 1/3 29 15 15 8 6.33 1-0 4-0. . Bob Welch 4 19 33 16 6 8 7.58 1-0 1-3. . Mike Mohler 2 6 1/3 6 2 1 8 2.84 0-0 2-0. . Curt Young 1 4 2/3 4 2 2 0 4.15 0-1 0-1. . Totals 20 103 2/3 140 76 41 57 6.62 3-7 10-10. .

# - Team record in those starts.