Boston pitcher Dennis Eckersley joined baseball's millionaires' club yesterday, one day after his fine opening victory against his old club, the Cleveland Indians, by signing a $2.8 million contract extension with the Red Sox.

The contract, spread over five years, will become effective in 1980.Eckersley, acquired from Cleveland last spring will receive a reported $185,000 from Boston this year under a contract signed when he was with the Indians.

The new agreement will make Eckersley one of the highest-paid pitchers in the game, said his agent, Ed Keating.

In Detroit, Rusty Staub's hopes for a new contract or team have come up against a stone wall in the person of Tiger President-General Manager Jim Campbell.

Staub, 35, is seeking a three-year extension of his current contract (he has two years left, each worth $200,000) and has refused to report to the Tigers until Campbell agrees to negotiate. Staub hinted that other clubs have contacted him.

"That just might be worth checking out," said Campbell, hinting at possible tampering. Campbell has repeatedly ruled out making a deal for Staub because of the Tiger slugger's refusal to play for Detroit.

"Even if I'm nothing to him now, I still have value," said Staub, who was the American League's top designated hitter in 1978 with 24 home runs and 121 runs batted in. "You can either leave something on the side of the road to rot, or you can make something of it.

"To let talent of mine go to waste would be a shame."